I agree completely. That would be terrifying. Not to mention, at that point it’d be nearly impossible to interact with Dean at all. Sam and Bowman would have to be his caretakers.
I can’t say how small Jacob will end up (can’t give everything away 😉 ), but I will say that being smaller than both Sam and Bowman will really mess with his head. Being so little in general will be truly terrifying for Jacob, who’s used to being a towering six foot five.