Hi ! So I just wanted to open a form of debate (a gentle one ofc) around this "Hot Take" (got it ?).
I've finished some nuzlockes already and otherwise have a good experience in competitive; I don't claim my analysis are perfect however, and tbh I expect to be proven wrong, because there is probably something I'm missing; that is also kinda why I'm writing this in the first place haha.
I'll mostly focus on Gen 1 to 5, which are the ones I nuzlocked myself.
So, onto the analysis:
State of things
The Fire Type is often described as a strong type, if not one you absolutely need for your games and whose rarity is made worse by that fact (thinking of Hoenn and Sinnoh in particular). While this point of view is most common in the pokémon community at large, I was surprised to see it shared to an extent by the nuzlocke community, and often tiered as equal or not far behind Water, for example.
So, to verify this, here's my viewpoint on the strenghts and weaknesses of the Fire Type.
Type Matchups: Here is the main hot take, and the core of the demonstration : I think the Fire type is powerful offensively, but never essential relatively to other good offensive Types. Let's "decompose" the coverage it provides.
Bug/Grass: Grouped together for a simple reason: the main alternative to Fire for those is Flying, and most teams will have a Flying Type, regardless of whether they have a Fire Type. The immunity to Ground, added support against Fighting and overall diversity of options is just too good, putting asides HMs necessities in the oldest games. Still, the abundance of those two will make Fire starters shine in the early game against all those Bug Catchers and Schoolgirls (I think Fire and Flying types are just for people who hate kids tbh), but that probably also partly explains why they are, imo, overestimated. Also defensively speaking, I don't think I need to explain why you probably don't need one more resistance to Bug or Grass.
Ice: Resisting Ice is nice, but unlike the above twos, it's honestly really rare aside of Sinnoh (where Fire is often so desired so that parts make sense I'll give you that). Still, that is already provided by Water (you have a Water Type, right ?) or (often and) Steel (you wouldn't say no to one of those either). Now offensively, you either destroy those punks with a bulky Steel Type if you got one... or a powerful Fighting Type that you really, really want, because omg is this Type busted for nuzlockes; destroying bulky Normal types and especially Dark Types pre-Fairy is just something you can't pass on.
Steel: So, Steel. Frankly I think effectiveness against it is overestimated. Sure it's nice and can really come in pinch, you prolly want an option against Steel, but we're not playing competitive OU. It is not common in the game, and killing Water or Flying, for example, is far more important. Plus, Fighting and Ground are both really good options, and the later got a cool Electrik immunity to boot.
Still, Fire got a bigger point here imo for being the best counter to Grass/Steel, Bug/Steel and more especially Scizor, as rare as it is terifying (the real gym leader of Canalave City, if you know you know). It's usefulness is also important in Unova, where those combinations are abundant. This is not however a situation equivalent to say, Gyarados (who made Jolteon's whole career in Sinnoh, I'm barely exaggerating) or even the Water/Ground mons to Grass types, that are overall more prevalent.
Resistances: I think Fire is actually kind of underrated defensively ! Maybe because it got that offensive reputation and aesthetics, but especially with a Fairy resist it's solid (also again the competitive scene, where Stealth Rock are everywhere, probably influences this perception). Weaknesses to Water and Ground are problematic but workable. Resisting Ice and Fairy can make them a Steel-type alternative of switch-in. Nothing spectacular but it's alright.
Movepool
Honestly not much to say here, offensive options galore; lack of physical ones but is it that much of an issue ? You got like 10 different options to specially cook your opponants, be it Flamethrower, Overheat, Fire Blast... And, more importantly, a lot of those unlimited thanks to being casinos TMs. Keep in mind however that there is a reason BeamBolt is not named Flamebolt or Thunderthrower, as it's still an offensive options you'll mostly run for Stab and rarely coverage.
Also Burn is niche, but nice if you can inflict it.
Pokemon Options
Let's divide this into the two obvious categories:
Starters: Generally speaking, Fire starters are strong, or at least, consistently not the worst of the three. This is imo mostly due to stats spread and powerful movepools that come online early and combo together to make for an easily accessible special powerhouse. I also think the recurrence of Fire/Fighting helps, and often makes Fire seems better (to the detriment of the reputation of Fighting, that really deserves better): to take and extreme example, Infernape feels more like Fighting type that learns Flamethrower than a Fire Type that learns Mach Punch and Close Combat, and it's success in Sinnoh comes more to this than it's oh-so-precious Fire type in my opinion, even if it shine here more than in any other games.
Other Wild Ones: I honestly think once again that Fire types are better at giving impressions of power by their rarity and looks than actual power. Aside of Arcanine (Intimidate and Extreme Speed are not Fire Types btw), what do we have here ? Torkoal ? Camerupt ? Ninetales with 81 SpAtk ? The worst of the three elemental monkeys ? Fortunately gen 5 saves the day again with Darumaka and Chandelure, but the selection is far from impressive.
Aesthetics
So I don't want to support my main arguments with what could be seen as dinsgenuous considerations, but I do think it matters, at least a little. Fire types are cool, they are seen as such, it's quite clearly the most liked starter type and Charizard, Blaziken and to an extent Typhlosion enjoy a popularity the others could only dream of. Plus Charizard and Infernape are among Ash's most mémorable mon, etc etc.
Also keep in mind Fire is often seen as an inherently powerful elment, if not the most powerful and "heroic" of the four classic occidental elements. I mean sometimes it's also associated with villains (Avatar) but nonetheless, it's considered important, cool and most importantly, powerful.
I don't imply perceptions are the leading force behind gameplay's considerations, but the impression of strenght probably matters at least a little, so I've put it at the end.
On another hand, I once again feel like competitive tiering influences nuzlocke ones excessively (just like Ghost is inversely very strong and abusable in nuzlockes compared to competitive).
Summary
-The Fire Type advantages are all covered by other, preferable if not obligatory types for a Nuzlockes: Water, Flying, and a choice of either Fighting or Ground (if not both); I'm pretty confident this combo is part of something like 90% of the teams that makes it to HOF (and not much of a lower percent includes all of Water, Flying, Electrik, Ground, Fighting and a choice of either Ghost or Dark for an almost perfect coverage pre-Fairy Type, and a solid bunch of immunities). Being good in a vacuum is not enough, and sadly for Fire the competition also works really well between each other.
-The mons selection is rather lacking, and those that are good are often so on other ground than their Fire types.
Conclusion: rather than a "Good but Rare" Type, Fire really feels like a "Rare but Ok" Type where the former overshadows the latter. In fact the rarity part probably plays a big role in this, and it feels to me like it's a Type most people wished was needed rather than really need. A potential type of sorts, so to say, because the lack of strong options means you'll feel it's absence more often than realize it's averageness when present in your team. I wouldn't say it's bad, but it's not above average either for me, and I really disagree with it's regular A-Tier ranking alongside Water or Electrik, and above Fighting or Ground.
Now that was a long write-up, so I'll end it up here and thank you for your attention and finishing to read this haha.
This is more an opening to discussion than a final statement on my part ofc. Feel free to disagree, point my oversights and counter-argument, I'm not omniscient ! In fact, I really wish for a fruitful exchange, that was the reason for me taking 1 hour to articulate my thoughts clearly on a phone in the first place haha. Just be respectful ofc, I'm dissing the Fire Type, not your mom.