Minato could use FTG before he hit puberty, so he's well versed in it now. There's no real statement that implies by this stage he doesn't have the advanced applications of FTG either, so not sure where you're pulling that from.
We also don't know when this happens in respect to the Ay confrontation, but that doesn't really change his strength. He doesn't need the respect of weaker characters to prove himself.
The timeline for when Jiraiya trained Minato is iffy, in relation to Nagato. But all things considering, they have very similar markings and Jiraiya was still operating with his team cell in Amegakure. This is more than likely Post-Sannin.
So even if he wasn't up to his Naruto standards, he's not going to be dramatically weaker.