Soler hasn't been *THAT* bad. He was like -10.7 UZR/150 in RF and almost all of the negative came from range portion. From watching him play, that seems more an issue with route running rather than speed. I mean he's not the fastest guy in the world but if he took better routes don't think he would look nearly as bad. The good news is that's probably something he gets better with over time and given his injury history in the minors it kind of makes sense that's not his strongest area.
I'm going to largely avoid talking about Baez because I've already made my feelings on him well known. However, I think you're vastly overrating his defense. To put into context what 2 fWAR looks like, Jason Heyward was like 2.3 fWAR between his baserunning portion and defense. And not to shit on Baez but simply put this widely held belief that he's a plus or plus-plus defender does not agree with the defensive metrics. Even if you go to the more rudimentary errors as a measuring stick, he's had around 12 errors in 600 innings between minors and majors at 2B and 102 errors in 3150 innings at SS. I will say from what I've seen of him at 3B he looks better to me personally there but he's only played around 150 innings there between minors and majors.
I wont get into a hitting debate on Baez because I'd just be repeating things I've already suggested. All I will say is we are 326 PAs in now and he has a sub 6% walk rate and a greater than 30% k rate(being generous).
Historically that hasn't worked out well for people. I'm still not 100% what to make of Soler as a hitter but his 7.9%/28.4% bb/k rate profiles much better going forward especially when you start talking he's at 10.9%/23.6% this year. He needs to get better defensively though in LF if we were comfortable with Schwarber out there I'm not really sure Soler is any worse.
Edit: One more thing. To contrast what an actual plus defender(Russell) looks like in the MI, Russell had 9 errors in 746 innings at 2B last season and 5 in 606 between this season and last to go along with 31 in 1926.2 innings at SS in the minors. Baez is basically 2x that at those positions. I just wanted to make that clear because I often get accused of needlessly craping on him but if this isn't fair I don't know what is.