*Sorry for the massive wall of text, tl;dr at the bottom*
I'm playing a Pathfinder campaign with some people and one of my friends is our "assistant GM", which according to him at character creation meant he's only going to be helping out with story writing and not actual gameplay. There are a couple of new players in the campaign with the only ones who've played before being the assistant GM, myself and a coworker of the GM (our GM has also played, but it's their first time running a game and despite that, they're doing pretty well at it).
First boss fight: we had 3 people absent, including myself, and our Priest (who probably has more experience than any of us, he's the coworker) hadn't joined yet. In other words, the assistant GM was the only non-first-time player present for the boss. My Psychic had the only healing in the entire party, so with me being at an Infinity tournament that weekend we lost that advantage as well. With just a Spiritualist, a Paladin and a Magus, the fight definitely did not go well but everyone present did survive.
Here's the problem I'm having though: from what I've gathered from our Magus filling me in, the assistant GM is saying he basically carried the fight. I talked to him about it, and he said that he had slightly god-modded his abilities to make his character a bit stronger "for the party's benefit", because "the fight was a complete disaster" (to which I will admit to saying basically "yeah, no ****, you went into a bossfight short your only healing, the tank and the DPS, what did you expect the supporting casters and brand-new tank to do to a Rakshasa?" in my head).
Though one was not actually relevant in the bossfight, the changes he made were instant and therefore uninterruptible phantom deployment rather than the normal one minute and being able to shift multiple mind affecting things onto his phantom that day rather than the normal 1 (this did not actually come into play). I asked him if this would continue to happen and he said the deployment thing most likely would but he wasn't sure about the other. Also, the see invisibility skill he gets at 9th level might be made passive rather than the spell-like, once per day, for ten minutes it's supposed to be. He was also given 1st-level Bard for free shortly after character creation (mainly, as I understand it, for Bardic Knowledge despite my Psychic already essentially having this through its Rebirth discipline), so he's basically a level ahead of the rest of us in a way that's trying to do what I was already doing, which definitely sort of annoyed me.
The whole "only helping with the story" thing has already gone out the window, and it's starting to seem like he really just wants to use his assistant GM status to justify his character being stronger than the rest of us. From my conversation with him on the matter, I could tell he most certainly did say he carried the fight as he was basically saying without his changes the whole party would have died (which would definitely not have happened had they waited to do the bossfight when I was available as, again, I had our only healing).
Both me and our Magus feel that in trying to "cover for our dysfunctional party", he's really just basically saying "you couldn't actually do this if it weren't for me and all this "help" I'm giving you by making myself stronger", and the whole Bardic Knowledge thing definitely contributed to that. Two of the other three had their first session with us last session, the session after the fight, and the third is brand new and doesn't really care either way as he's still trying to figure everything out, but the Magus and I are getting a bit annoyed.
I'm not really sure how to handle this. I don't want to be a jerk to the guy, he's my friend, but I don't feel like buffing his character by changing the wording on its abilities to make them better is the right way to handle the situation. Would y'all suggest we just accept it and move on, or is there a specific way I should go about handling it?
tl;dr: Assistant GM god-mod-buffing his own character by tweaking its abilities because he felt the party was incapable of beating our first boss fight if he didn't, despite going in short the only healer we had as well as our best tank and our only DPS.