There are 2 types of mechanics: those that the game expects you to use and those that it doesn't. It is fine to simply ignore the latter type, but ignoring the former type can adversely affect ganeplay.

Example: Eating Pigs Heads
1.) If Larian balances all combats assuming that players will eat a pig head to restore 15HP every turn, then not eating pig heads will make the combat incredibly more difficult. So you have the option of
  • a) eating an entire pig head in <2 seconds, something that is incredibly un-immersive
  • b) playing an unfairly balanced game.

This is a BAD implementation.

2.) If Larian balances combats assuming that players won't eat a pig head every turn, then eating pig heads will just be a way of optionally making combats easier. This is a GOOD implementation. I personally don't understand why it's included in the game, but it doesn't affect me.

Many of Larian's homebrew fall into the former category. E.g.:
- Enemies use high ground, so you can't ignore it. Enemies also sometimes use shove & backstab, and multiple enemies have been given jump+disengage powers.
- Encounters are balanced around constant advantage via high ground & backstab, bonus action jump disengaging, and BA shoving. Enemies are more powerful than in PnP 5e because we can do all these things.
- Companion dialogues are tied to long resting, forcing the player to rest or miss content

Saying "just don't use these mechanics" is ignoring the problem; that the game is balanced around using these mechanics. And, in my opinion, using these mechanics makes the game more boring, less tactical, and less fun, but not using them makes the game unfairly difficult.
You can argue that you personally don't think these mechanics make the game less fun, but that's only a relevant argument if you think Larian's implementation is better than the alternative. Otherwise, if you don't care, then why are you arguing for it?

To mention the BG2 cloudkill example, a more apt comparison would be if combats on normal difficulty in BG2 were prohibitively difficult if you didn't Cloudkill-cheese and/or if the enemy AI would use this strategy against you. In those cases, not using cloudkill would make the game less fun, but using cloudkill every combat would quickly get boring.