Question:
Do those who dislike minions also dislike scenes in books of movies where the hero(es) defeat multiple guards/thugs/etc in rapid succession, but still taking time to parry their blows as if they were credible threats, but then when they reach a named villain it takes them several minutes of screentime/paragraphs to defeat them, usually taking a wound or more in the process?
It seems to me that these are a staple of many genres, including sword and sorcery and fantasy, and that a gaming system unable to reproduce such a scene is lacking.
By allowing the minions to have level-appropriate defences and attack bonuses, we are able to understand why they remain a credible threat, even if they lack the fortitude to take a single blow, or the luck/skill to not present an opening for a lethal blow. Furthermore it even explains why 0-level commoners were helpless against them - they needed a 20 to hit.
The only problem lies in if a minion transforms into a non-minion, or vice-versa. Again, a non-issue IMO. A minion can only survive if it never got hit. So the only way a minion can be encountered as a non-minion is if its minion status was never confirmed in the first place. *Dramatic unmasking* "HaHa! You fools! You thought you faced a common foot soldier? I think NOT!" (And the PCs attack because nobody likes a mouthy mammoth. )
The other way around ought to be reigned in by the fact that it is often poor storytelling.
Consider: any major character who has survived previous rounds of combat with the PCs needs to have a damn good reason from the DM for being killed by a single blow because it has the potential to be jarringly anti-climatic. So such characters should probably be either weakened somehow (injury, poison, illness etc) or else suffer some form of treachery if they need to be 'written out'.
So minion rules should only disrupt suspension of disbelief if they are used for reasons other than intended: to recreate scenes where the heroes fight through a large number of minor opponents to reach the real threat. This intended use is such a staple of the genres D&D handles that any gaming group ought to be able to take it in their stride.