I'm of two minds about this. From the perspective of executing a design DST is doing a great job. For example, the QR suits from Endgame are really well done as far as tampos and paint go, they're just not very accurate to the movie because they used concept art. As a package though I'm consistently finding current minimates disappointing. I think alternate parts and effects stands gave this line a lot of it's energy and the build-a-minimate has taken that away. Instead of wave 48, where I didn't really like the costumes but ended up loving the wave, there's 78, where I liked the costumes but ended up being indifferent to the wave and thought Multiple Man was an embarrassment. And, yes, I know a lot of collectors will disagree with me because they prioritize quantity of characters over everything.
As far as DST not changing things up more, that's easy: It's just not worth it, there aren't enough of us buying them. It's wishful thinking to assume there's some sort of silver bullet that will turn minimates into a sales juggernaut.