I do not understand this reference.
But considering Main Character Syndrome is a frequent insult, this is like calling a turkey a turkey. Sure you used the insult as an insult, but what the heck is the turkey supposed to do and why should it feel bad for being what it is?
I'm not aware of a term specifically for that kind of behavior pushed too far but main character syndrome is close enough in enough ways. There was silliness & an expectation of an understood Overlord reference, I'll try to shed light on the reference.
Ainz Ool Gown is the name of the main character from an anime/book series called
Overlord. There's several novels to it with a lot going on plotwise, but pretty much a guy gets isekai'd into his max level mmo character complete with
levels gear & stats as is. Along with him are an enture guildhall worth of equally overpowered somewhat insane power hungry NPCs. The whole gaggle of them find themselves in a standard d&dish world where the people & the world have levels gear & stats closer to standard d&d levels. Throughout the series being undead is sapping away Ainz's ability to feel empathy & such he plays off fear of other players in a similar situation with a more PvP focused build to keep the guild's bloodthirsty NPCs from just massacring everything as he slowly takes over the world. The author started writing it after being unable to find players for his d&d game post graduation & it's chock full of what were probably PCs/NPCs from his past games. Think of
record of lodoss war (it was someone's 1e/2e campaign log turned into an anime) but replace the party with an absurd GMPC with a bunch of similarly powerful but insane & unhinged GMPCs to do the tedious plans for him that players usually farm out to NPCs.
The power delta between Ainz & his associated isekai'd NPCs stacked against rest of that world is
as massive as you would expect (if not moreso). Without needing context NPCs they like rehind their back to them like
this 
. Rather than plot armor they are just
that far beyond everyone kind of like high level PCs can use their strength to treat nearly anyone without
deific levels. Because it's a story (or campaign in a trrpg) the world needs to somehow carry on no matter how those actions twist the world around & in Overlord it does.
If a player is acting in a way too far into the idea that the PCs are the plot armored protagonists of the world itself enough to ask a question like "
Is it really 'Main Character Syndrome' when you're literally supposed to be an ensemble of Main Characters?" it's kinda channeling Ainz.
