Thats not entirely true. I dont think Cerebro needs Xavier to actively download everyone's memories; it does so by itself. Your theory isnt a bad one but I think its makes more sense that Xavier didnt restore him to how he was when he left the planet in DG. Vulcan was a sociopath and if they brought him back like that, he'd need to be caged bc he would destroy Krakoa out of spite. If they restore him to how he was prior to his original "death" and slowly explained things to him, I think that would have set up up to be a sane functional individual