Dalbec's bb rate has been 11-15%. WMD's was 4-8%. They really aren't the same hitter. Dalbec walks more and has much more power. WMD had good power. Dalbec has elite power.
It remains to be seen what they do with Wander Franco. It certainly looks like they messed around with service time the year they brought up Snell. Adames probably should have been ready opening day in 2018 too. Archer in 2013?
If they need an additional starter, they'll use Andriese. The first guy up in an emergency situation would probably be Gossett. They also may just go with bullpen days as they have in the past.
There's a non zero chance that Dalbec is hitting .200 in July. If that happens, Casas will have every opportunity to come up, especially if the Sox are competing.