On the principle, I broadly agree with the view that "you should take responsibility for playing the game the way you want so that you enjoy it", which I feel is an equivalent formulation of "if you don't like this feature, don't use it". And this for the very reasons you mention : this is a SP/coop MP game. But I think it applies in some cases, and doesn't apply in other cases.

Some cases where it applies, and I'm not bothered in the slightest :
  • Eating food in combat.
  • Barrelmancy.

Some cases where it doesn't apply.
  • High-Ground rule (even if you don't use High-Ground, you'll at least have to prevent enemies from abusing it).
  • Rest anytime.
  • Characters out-of-combat being on a different timeline.

For rest, it's currently a case of incomplete design and it shouldn't be up to players to finish the game design (Nick Pechenin once explained the system Larian was thinking of doing for rest, hence why I'm fairly hopeful that this is just a case of not-implemented-yet). Consider a single-player "platformer with enemies and damage". When you have taken a certain amount of damage, you die and have to retry the current stage/level. Now imagine that the game does not have a damage threshold and lets you decide dynamically when you took too much damage and should restart the level. That's bad. I'm all fine with a difficulty option where I can set the threshold higher or lower, prior to attempting the level. But the designers should provide a default setting for this threshold, where they think the game is a nice and challenging experience for most players.

As for character out-of-combat being allowed to take as much time as they want, I'm completely unbothered by the fact that this can serve as the basis for an exploit.

However, as I explained above, the problem is that the current system can be quite penalising for a player who didn't even remotely try to exploit it. As soon as you start sneaking into position to ambush your opponents, you are exposing yourself to a range of difficulties. Your characters are not guaranteed to be all drawn in combat.
  • Characters who are drawn in are out-numbered, and thus more likely to not be in a good place in the initiative track, and get slaughtered before it's their turn.
  • Characters who are not drawn in lose their buffs at super-fast speed.
  • Characters who are then "late to join" (although they weren't realistically late and the player certainly didn't mean that) will be robbed of their turn in the round where they join.

These are the problem to solve. Not the fact that exploits are possible.