We have to remember that the J-35 is meant for the PLAN. So, a lot of the key changes can't have anything to do with the PAF because the PAF doesn't have aircraft carriers. Stuff like a specific landing gear, stopping salt erosion, etc don't apply to 80%+ of the PAF's fighter fleet. It's unlikely we'd recommend or foot the bill for those.
I don't think we could've offered much input to the Chinese either. The FC-31 was probably fine the way it was, but because the PLA hadn't adopted it, the PAF wasn't sure of its viability. It's one thing to co-fund the JF-17, but to just complete a FGFA is a whole other ballgame, financially speaking.
But now that the PLAN is moving ahead with the J-35, I think the FC-31 has enough 'lift' from China for the PAF to seriously consider it.