Much as I love many aspects of PSP hardware, that simply isn't true. It's a lot easier to extract performance from, and it's generally(but not always) the "smarter" hw in terms of resource use, but the upper limit just isn't there to beat the PS2.
(not really sure how gameplay enters this equation though - but if you think PSP controls are superior you could always make PS2 game use PSP as the controller

).
That entirely depends on your content creation pipeline. I think the problem is more with sharing more of the codebases then applicable/beneficial.