I don't mind killing Adam in V6 as part of the rewrite, if anything I feel like RWBY proper should be axing one villain a season anyway. Which is something Raymond hasn't fixed, again, but even made worse since he decided to keep Roman around.
What he fucks up is making it a team battle where Ruby kills him. A team battle could kind of make sense, I suppose, but by handing the kill off to someone completely unrelated to him you rob the scene of any emotional catharais whatsoever. Blake and Yang killing Adam together is the culmination of three seasons of development for them and their relationship, a literal representation of them killing their past and overcoming shared trauma together.
Raymond, who has the literacy of a mongoloid, obviously missed all this so I'm not surprised he fucked it up in favor of making Ruby shoot him in an act of reflex because... I dunno. Shock value? To give her something to do? To try and fix the problem of Ruby not getting to do much in the show? (Even though V6 is ALREADY one of her better seasons, as she gets to heroically defeat both the giant robot and master her silver eyes, both things I think he changed if I remember right.)
That's not to say the main show handles Adam being killed particularly well in the aftermath, since it weirdly never really brings up the kill ever again, but it at least had purpose.