I don't think I've seen a valid argument as to why the cheese is good for the game from the people defending it or being neutral to it, beyond "lolz" and "doesn't bother me". All other considerations be damned.
Well, I have read many times that barrelmancy, aoe surface spam, height and backstab advantage would add extra layers of complexity to the game. Then there were many people painstakingly pointing out that this '+1 extra layer to complexity' was actually more of a '+1 -10' to complexity because of dozens of spells and abilities being absolutely devalued by these fundamental using-the-sledgehammer-method changes. But those kind of objections are being blissfully ignored for the most part.
I think these people have a fundamental "moar is betta"-mindset pretty much void of nuance. They see something they had fun with once, and it's all good in their book. Added complexity isn't necessarily a good thing though, to the contrary, I would say much of it, the needless parts, is a negative given how ENORMOUSLY complex D&D already is. That said, I don't mind the core premise of much of this, it's just the enforced, clumsy implementation of these things as core mechanics that I object to.
For instance when it comes to height and flanking advantage. Incentivizing tactical movement is a GOOD thing. This is something D&D used to have, but that is largely lacking in 5e. This was the not-so-secret-sauce that made combat in DOS2 so fun. However, incentivizing it to the point of making dozens of spells and class abilities redundant, is clumsy.
Flanking in particular comes with an additional set of immersion and balancing issues. Firstly, how consistently the enemy AI fails to exploit it, while they prioritize height advantage too much - as to run far away from near melee to climb to a high vantage point. Secondly, how the AI is unresponsive to flanking which kind of highlights that turn-based combat (which I prefer) is a really unrealistic approximation of real combat.
I would love to see enemy/friendly AI react to flanking -even not on their turn- by pivoting around to face a -single- flanking threat, as to require two threats or surprise to gain a tactical bonus (smaller than advantage). When a bonus is all but guaranteed, having to repeatedly micromanage to get it, feels like an annoying waste of time. Entitlement sneaks in. If you have at least to make a tactical effort requiring more than jumping in or moving at the back with a single character, you feel appropriately rewarded.
Barrelmancy is largely fine too. Just scale it back from being a core mechanic to be a situational tactic (this involves fewer placements and much less room in inventory to carry these around). Dipping weapon could be less cheesy and micromanagement heavy by scaling it back to affect arrows/bolts only, while also including any of the dozen alternative ways in D&D to enflame weapons. Anything but the ever-burning candle that can be fetched from your endlessly large inventory in the midst of combat!
