If you cannot play without minmaxing is really a you thing, the fact that you can get better stuff if you kill everyone doesn't mean you HAVE to do it xD. Usually killing everything gives you more XP than defusing a fight through diplomacy but if you don't level up by milestones is hard to balance, specially if you can get xp from ability checks and then kill everyone in sight.
Again, it's just a minmaxing thing and as everything else I think that having the option to do it is always better than having no options.
