There are plenty of pitchers who can have successful careers as MLB relievers, who simply cannot and will not ever be an effective MLB starting pitcher.
I'm not saying Hall is for sure one of those, but it's certainly within the realm of possibility that he can't be "fixed" to be a starter and at some point we'll have to embrace what he can do rather than changing it.
Seems like only yesterday that some of us were adamant that Josh Hader belonged in the rotation because we didn't want to lose out on the next Chris Sale. The best thing we ever did for him or us is to just let him be Josh Hader and not try to turn him into Chris Sale.