He's much more suited as a 4C at this point but he at least fits how Sullivan wants to use his bottom-6. It's not going to be miscasting Brassard or Carter in a defensive 3C role anymore, so there's at least that.
If he can give 25 points while not hemorrhaging goals against, I'll be fine with it. I definitely won't be happy about it unless he produces like a legitimate 3C, but I'll be fine with it if he can at least be good defensively.
You don't necessarily need a HBK Bonino style performance out of your 3C, a 2017-2018 Sheahan performance is totally acceptable.