Although I disagree vehemently with the OP on his crusade against the genre (especially when it comes to the extreme non-linear open-world trend which in reality too often boils down to quantity over quality), he's not without a point when it comes to flow of combat. A great many of the current issues is caused by Larian's early decision-making.
For instance, having a proper day/night-cycle with exhaustion and long-distance spotting of light-sources would lend the slow pace more credence. Camping, rather than be seen as an obtrusive mechanical limitation like running out of spell slots, would naturally weave the 5e system mechanics into the story-telling.
Another issue is Larian's design vision of making interactive systems. Worked fairly well in DOS2 (though I was never a fan), but less so when shackled on top of an already overly complex system such as 5e. You have an over-abundance and increasing amount of options that all somewhat slow combat down. Besides giving an impression of gameplay that lacks polish.
Simple streamlining is still largely absent. The dash animation wastes time as well as looks unimmersively magical. My favorite dead horse to flog is the Warlock Hex spell which easily could make the ability score debuff automated and thus remove an unnecessary timesink - which is the worst offender when it comes to slow flow of combat.
Are we still calling it the Divinity Engine? Has Larian renamed it yet?
Divinity 4.0 is the current iteration I believe.
