Okay two things about Hojo. He's Sephiroth's dad. He's insane.
One thing though, what strong will? Sephiroth is insane! It's also a stupidly huge coincidence that the one person Hojo used for that experiment happened to be the one person with the insane amount of mental ability to control ancient super powerful aliens after being driven crazy,stabbed, then stuck in mako for a few years.
You haven't explained why Sephiroth would go to the extreme lengths of projecting his image, to manipulate the appearance of Jenova (an ability that solely belongs to Jenova and is never suggested to be passed on through cloning). He didn't want his face to demand respect, those that knew him he killed. Those that failed to recognise him, well failed to recognise him. Only Cloud and Co. really have frequent encounters (as far as we know).
The game, from beginning to end is about the reunion. This is solely to do with Jenova. Sephiroth just happens to have a lot of her cells.
I do have a theory as to why Jenova appears as Sephiroth, that extends the luring Cloud theory. However this theory requires a lot of theorising outside the game, and as there is no decent explanation from any side I'm not going to distract the topic by bringing it up.
