So, just to clarify, I think Steiver is more talented and has more potential to be a dominant player. I think Walker is a pretty boring player. However, there is two years of health, of continued work on control, of developing pitchers, that makes a list of a lot more work Steiver needs to do to hit that higher ceiling.
Dunning was awesome in A+ as a college draft pick. Then he had a series of injuries which he can still come back from but he's likely not to start his mlb career, if he does, until 26.
Walker, by contrast, is entirely competent if not exciting because he has only a 15% k rate and a good 9% walk rate. He, from accounts, still has not failed as a CFer. That's the makings of, at least, a borderline MLB player.
Now, I've discussed giving value to players who merely make the big leagues even if they aren't particularly good, but walker has a very decent likelihood of having a big league career (any version of one).