Regardless on the fact that its Ubi's fault it is still in sony's best interest that this game runs at least at parity, for the reason that this creates only negatives for sony.
Sony can do and maybe should nothing, but if they do nothing they will suffer slightly for it .
We don't know how things went behind the scenes on this matter.
What if fixing the issues required extensive mods of key parts of their engine and Ubisoft couldn't afford to do that because they wouldn't meet their deadline (which is clearly more important than quality for them) ?
It's not like Sony can force them to do things that would disrupt their production pipeline.
We don't even know if they wanted to be helped at all!
Maybe they just settled with parity in mind since the beginning, XB1 was the lead sku and got all the attention, PS4 code is probably based on some kind of unoptimized PC code intended to run at the same quality settings of the XB1 version. Eventually they run out of time, the game needed much more than a 2 weeks delay to be completed and has been released as a 20fps mess full of bugs on both.
Again this is all speculation, we don't know what happened with this game, the deals they had in place when development started and so on.
Still considering the backlash they have faced since they mentioned resolution parity one month ago....they have probably realized that they have fucked up and things didn't go well for them using this strategy.