Let's test your theory. I start in 2002 where fangraphs started tracking velocity and make an exhaustive list of pitchers who average 94+ on their fastball and get over 58% groundballs.
Ready?
Here's the exhaustive list:
1. Aaron Sanchez
That's right, there's nobody else. You can lower it to 93 if you think he loses velocity, still nobody. Hell, I could only find one individual season in that timeframe and that was 2007 Felix Hernandez.
There just aren't many pitchers with 3 key things that Sanchez possesses. Those are stamina (maintains 94+ up to 100 pitches), extreme groundball ability, and great velocity. The strikeouts are a concern. The walks are a concern. If you doubt that he is capable of fixing it though, look at his command in relief. I don't expect a big change, but there's some potential improvement to be had.
Let's not waste a unique talent, especially with that all gold glove caliber infield D that we have.