I think you're disbelieving it for the wrong reasons. The biggest problem and one which Mugasofer mentions in his comment is that there's no set up system or reason for Quirrel to be remote controlling his body. Horcruxes don't really work like that in Canon, and it also doesn't match what we see: eg Quirrel doesn't take hours to respond to every single thing. It's possible zombie-mode is some sort of "cloud uploading" process by which he sends memories to his Horcruxes but it doesn't really seem like that would be affected by this sort of thing.

I think it's more likely that Pioneer is just a badass way to make a Horcrux and that zombie-mode is a consequence of something else, probably his mind-control battle with Quirrel or whoever Quirrel used to be.