I think one of the main improvements we've - interestingly - been unable to widely adopt is an actual live programming environment. Smalltalk was this. Nowadays I mainly use Common Lisp for something reasonably close.

We're still mostly stuck in an edit->compile->test cycle. Stuff like TDD and debuggers help here, but considering the untapped potential for what programming environments could be, it seems to me like we're stuck on a local maximum.

Edit: Don't get me wrong, programming in Smalltalk didn't seem entirely pragmatic to me. Reproducibility becomes something you need to actively worry about, with popular tech stacks it's kinda built in. My point is the potential of such approaches, not the pragmatic viability of the implementations we've had so far.