Is Doom 2 Bestiary the most varied bestiary of any fps?

ivandobrovski as a friendly advice, i suggest not assuming things about other users outside of the proposed discussion in order to make your rebuttal - otherwise you're risking creating a strawman to ground your defense and if you spent some time 'round here (or in anywhere else for the matter) you'll know that this kind of approach is the primary cause for discussions escalating into name calling. Yes, this is the internet so you should take any claim and/or personal experiences that are brought into discussions with grains upon grains of salt - as they might be just fanfics manufactured on the fly for trolling purposes. Still we owe at least a bare minimum amount of credibility to each other words.

So to clear things up: No, i don't have any rose-tinted glasses for Doom, specially for Doom II since i only properly played the game from start to finish in my mid 20s. If i would have any kind of nostalgia bias it'll be for the classic build-engine games such as Blood, Shadow Warrior, Duke3D, Redneck Rampage and NAM (or even for Heretic) as i grew up playing these games (way earlier than i think i was supposed to) and despite other modern "cool looking" fps games of the time (Quake, Unreal, Half-Life, Counter-Strike, Serious Sam, Will Rock, Halo, Killzone, CoD, etc) i've always came back to play Blood, SW & cia while i completely lost my interest for Doom over the years until i've discovered mods like Brutal and Complex Doom that rejuvenated my interest for the game.

TL;DR way before playing Doom II and being properly introduced to it's new bestiary, i've spent countless hours investing my gaming time into other shooters.

Back to the topic. As other users like @vigilantdoomer and @pistoolkip pointed out, not only you're oversimplifying things but you're also not taking other elements of the game into consideration. You've framed the discussion in a arbitrary way that only the enemies that have some tricks matter while the rest are reduced to bland variants - while failing to take into account the support role the so called bland variants have, their particular strength, placement or even the tiers of escalating threat relationship between archetypes (like the imp>Caco>HK). So if you gonna discard all of that, why i should think that Duke3D, Quake or Serious Sam bestiaries are varied? I can reduce their enemies to simple bland varaints aswell, since the vast majority of the enemies don't have cool tricks up their sleeves and even the ones that have i can simply reduce them to a X + Y formula like you did with the arachnotron.

Other users such as kvsari , 40oz and joe-ilya also pointed out the anachronistic unfair unbiased frame you're giving to Doom's bestiary. In other words; you're judging and dissecting Doom's bestiary based on games that came after Doom, have different engine capabilities and that were ultimately build upon previous fps enemies (incl. Doom). All fps games to this date uses the very same concepts of Doom's monsters roles to give to their own monsters. But using your "method", i can pick Halo and just say that since every Covenant enemy is projectile-based then all of them are just less retard variants of grunts and every Flood enemy are just full retard versions of USNC marines + spawning capabilities. And if you gonna ignore the tiers of escalating threat of archetypes (i.e. reducing every projectile-based enemy to imp variants without taking into account different attack patterns, additional properties such as flying, both cqc and projectile-dmg output, HP total, etc) i can do the same for Quake or Serious Sam. The discussion become sterile, as you already have an arbitrary view over the subjects from the get go.