Two cents? Looks like something equivalent to $5.50 or so...
And reading through it... it makes a hell of a lot of sense. I agree with you on this. But anyone who has read the comics, will already know how powerful she can be without seeing it on the screen. As for the people who haven't, I think many would still understand his actions.
In that specific scene... where Jean says the Prof. is teaching her to develop it... that says it all. It shows how much he cares for Jean. He put the blocks in her head with the best intentions and followed his actions through by helping her to control that power, until the day it was released, so when her full potential came out, she'd be able to control it... not the other way around. I don't think he intended things to work out the way they did. He wanted to cage the beast inside her and help
Jean (not the Phoenix) develop her power in the concious part of her mind, so that when her subconcious powers (the powers of the Phoenix) were released, Jean would be strong enough to control them. There's that, and also I don't think that he intended for his psychic blocks to last forever. He knew eventually that her true potential would be unleashed... that's why he continued his sessions with Jean... to give her
control.