This year is a reminder you need 8 starting pitchers. Flaherty has an interesting decision to make. Don’t think you could get anything better for a 1 year contract so I prefer him coming back.
skubal, Olsen, Mize, Melton, Flaherty (or replacement FA) with Urquidy, Jobe, SGL, Montero as depth seems perfectly fine to me. Verlander would actually be a great fit as a reliable arm and maybe helps you limit innings for Melton and/or Jobe if necessary.
Bigger issue is the offense. McKinstry, Baez, and Wenceel are best as bench pieces. There is going to have to be a trade with Max Anderson, Jung, Lee, plus Ibanez and Vierling all competing for bench spots.