underused: firebat, optic flare - its very situational or used for fun
Plenty of units and skills like this in WC3 as well. Look at Necromancer. Terrific spellcaster on paper, Cripple is a great debuff. Not played ever, because skeleton spam gets countered by a Wand of Negation rather simply. Firebat still owns the shit out of heavy Zergling all-ins and is meant, very specifically, to be a
specialist unit, dispatched on very specific missions. Even if you gave the Firebat normal damage, it would still be liable to getting kited or simply destroyed by siege. As it stands, Firebats are really good for killing Zerglings, Zealots in team games (where you often go M&M), tanking Sunken Colonies when doing early Sunken busts, and for dropping into mineral lines to kill peons.
On the flipside: Look at how poor the Night Elf early game is, with Archers being an overall crappy, stepping-stone unit and Huntresses having lost much of their allure as a massing unit. Or look at how underused Hippogryph Riders are.
Even Humans, who are generally well balanced, don't see too many Riflemen simply because they become irrelevant in a DH/BM meta. Somewhat akin to how you almost never see infantry units in TvT and TvP because Marines quickly become outdated in the face of powerful AoE splash damage siege fire or spells such as Psionic Storm.
And heroes? Just look at the WC3 Night Elf meta where Demon Hunter is the best starting hero ever and the other three are almost irrelevant to the point where Nelfs generally prefer to hire the second hero from the tavern, with the Warden being notorious for her very high skill cap and thus unwieldiness that makes her a not very reliable pick.
Look at how Orc was infamous for being "Blademaster and Friends", where it's obvious 90% of the impact on the game is from BM bonanza.
Look at how troublesome UD in general was, and how little Dreadlord brought into play because in spite of a powerful level 6, he's hardly ever picked over the standard coil/nova because he gets shit on, and UD meta has been considered stale and one-note for many years now.
Your old post also asserted that underused units are:
which have recently had a massive resurgence in ZvT because they allow for a fairly cost-effective sweep of Siege Tanks in case of heavy mech play from the Terran,
which we all agree on, but bear in mind that Scouts are actually strong units
if there's heavy air-play. And there often isn't. Still, Scouts would be plenty viable for killing something like mass Battlecruisers or Carriers. The meta simply isn't oriented much about those.
Corsair with 5 dmg is only useful due to Web.
Web is almost never researched because it's unwieldy and fairly low-impact in most hands. What you build Corsairs for is PvZ because they're cheap, fast, and absolutely ruin any Muta based play, and they're almost always guaranteed to kill off at least 1 Overlord. Corsairs are a staple PvZ unit and are honestly in every PvZ game.
The Fantasy build in TvZ was specifically made to include Valkyrie against Zerg because Valkyrie puts on a ton of pressure, killing Overlords and handily countering Mutalisk play once Valkyrie get larger in numbers. Valkyrie's use has skyrocketed since this invention. Valks are also not bad in case of heavy Wraith play in TvT as support units. As for Devourers, they're a viable spenditure to get some use out of your Mutalisks after their window of opportunity has been exhausted. I like using Devourers in ZvP because I'm, personally, garbage at dealing with Corsairs, and Devourers are really strong against those. Devourers are also strong in the event of
extremely late-game ZvZ, because Mutalisks are a staple unit there, and Devourer splash attack + debuff is genuinely really scary in those engagements.
Citadel of Aldun being filler structure with solely purpose to delay access to Templars and archons is remarkable sample of great design
You also make CoA for the Zealot Leg Enhancement, which is a vital upgrade for all sorts of timing pushes and for overall increasing your Zealots' viability in the late game. Very often you have Leg Enhancements researching while TA is still being created. That's like complaining that Barracks in many TvP and TvT games only exist to force you to delay Factory.
Everone who praise BCruisers for their Yamato gun "oh how lovely it destroys that tower from safe distance",
That's not the primary purpose of Yamato Gun. The primary purpose of YG is to use in heavy Battlecruiser vs Battlecruiser fights, and to snipe units like in heavy fortified Siege Tank positions without putting your BCs in jeopardy from Gols and Turrets. You can even use them to shut down an expansion, as a few Yamato Guns simply eradicate CCs. Battlecruisers are a really good unit in late-game TvT, as it's often the only stalemate breaker in this heavily positional matchup.
should be nuked by ghost together with their eco- turtled bases. BC are one big resource dumpster.
So are Ghosts and their Nukes. Nukes are painfully situational and a high-risk-medium reward play in many cases. You have to take a detour for Ghosts which don't have a lot of room in many games where you rely on making a ton of Factories and Starports rather than Barracks. Ghosts cost high gas for what they are. Ghosts are poor DPSers. Lockdown is micro-intensive. Nukes cost 8 Supply and quite a hefty mineral/gas cost and they're liable to simply whiff the moment the Ghost dies.
carriers are perfectly balance
Yes, they are. They're only particularly notable in PvT, where they are tricky to deal with for Terrans. PvP? Arbiter Stasis Field + Psionic Storm + just mass Dragoons (which are a staple of PvP) completely annihilate them, and you're almost never reaching a critical mass of Carriers in PvP anyway because they're a resource dumpster. PvZ? Plague destroys them. Dark Swarm renders Interceptors useless while Hydralisks plonk away at the Carriers. Devourers kill them while being cheaper. Carriers, in general, are really poor units on maps with open fields because they rely on being outside of everyone else's LoS while the Interceptors cause mayhem. Even if a map is particularly cliffy, mishandling your Carriers means you will lose them to concentrated Goliath fire or whatever else is there.
Did anyone remember Zerg game without Mutas?
Plenty. It's common to not go Mutas in ZvT if you are not comfortable with your Mutalisk micro, and going 3 Hatch Lurker is plenty viable in such an event. Heavy Muta harass based builds in ZvP have fallen out of favor because of Corsairs. ZvZ is the only matchup that sees Mutalisks in every game.
Yes, it's a staple unit for anchoring on positions, overall defense, and, well,
sieges. They also suck shit in small numbers and without support from other units they are sitting ducks. Why is it wrong to have a staple
mid-game unit, again? Why are you not complaining that there are virtually no SC games without Zealots or Zerglings being made throughout the entire game?
stimpack+medic - its a MUST in every game
It isn't. You just do not go for excessive infantry at all in TvP or TvT. You make enough Marines in TvP to defend against Zealot rushes at most, and you make maybe like 1 Marine to kill off scouting SCVs in TvT. Any infantry-heavy strategies in either of those matchups are considered cheese due to how infantry-based play straight up ends the moment the opponent gets to his Advanced Buildings tech.
I can choose or omit any of W3 units, and this way of playing can be viable, unless maybe some pro level, that everyone here appears to be at - but i'm not following e-sport, nor i'm interested on receiving brain-damage from any "competitive" community.
I'm afraid that what you're attempting to say isn't "heresy". You didn't come here with a strong understanding of what you're talking about, and you just openly admitted that not only do you really not care how the game is played in multiplayer, but that "brain-damage" comment is probably meant to give you some sort of sense of superiority over people who actually research and play the games. You are not Martin Luther hammering his 95 theses to a door of a church. You are acting like a Flat Earther at a SpaceX convention.