Watching that DOS2 video does provide some clarity into their design decisions.
I think being able to screw your party members over is a completely different game. And it brings the question, is it worth the dev time to develop two different games into one? A story driven party based RPG, and a goofball mess around game where you are hindering other players rather than working together.
How are you going to be able to progress in the story if you're focusing on messing with your companions? Unless also combat is made trivially easy through cheesy exploits, so the goofing around does not make it impossible to continue the storyline. You can always toss a few barrels to solve a problem or just metagame or alpha strike the hell out of encounters.
Funny thing both was possible in BG1 and BG2. You could screw over companions; it was a very popular solution to get rid of one the pair and keep the other one (Jaheira or Khalid, for example), either by killing them or locking them in a building, because the other companion would not care. It worked because BG1 had no reactivity to that.
Same goes for ease of combat. Unless you mod the games, but those difficulty improvements are all thanks to mods, not the developers. BG1 is easy because of fireball arrows and wands, and BG2 because the arcane spellcasting system is ridiculously overpowered.