Even if the stormtroopers all die at the end of the movie anyway, I’d still prefer to get the impression that our heroes aren’t quite as ‘shoot first, act questions later’ as they come across in TROS.

It didn’t bother me to see troopers getting shot on Takodana in TFA because it was an active firefight - similar to how we all know that Luke Skywalker probably killed a few innocent people when he blew up the Death Star, but it was that or watch Yavin IV explode, so we don’t come away with the impression that he’s a cold, desensitised killer. But when our heroes in TROS run out of the Bestoon Legacy onto the Steadfast, guns blazing, blasting two FO troopers who have up to that point done nothing except ask for their credentials, and proceed to wipe the rest of the room out without flinching, it’s shoved right in the audience’s face. In TFA, a lot of edits trim Finn’s willingness to shoot his former colleagues, but there they were at least already shooting at him.

I mean, regarding the OT, Lucas has mentioned that “we very consciously didn’t kill very many humans in those movies” - this is obviously an absurd statement, but I think what he’s getting at is that you don’t necessarily get the feeling that the heroes are killing people. I suppose that’s why he chose to go with battle droids in the prequels, so that moments like Anakin killing Dooku (or Tal Merrik, Trench etc. in TCW) could stand out more.