Wait, wait back it up. Yu mentions the fight that him and yosuke had at the riverbed. That only happens in his rank 10 social link. So why the hell does yosuke have jiraiya and not susano-o?
In an interview, they stated that they kept all of the personas as their base forms because they're easier to animate and generally cleaner looking than the evolved forms.
I once read that if a persona isn't used for a while, it ends up weakening. That's why the P4 cast has weaker forms, because without the TV world, they had no reason to use them. On the other hand, the P3 cast were still actively using their personas, hence why they're personas stayed in upgraded forms
