Gammadoodler
Hero
It definitely borks the pet builds pretty hard, and layering it through glyphs means you can have more in an area than can reliably be dispelled.LOL, brilliant, while he might have True Seeing, keeping it going would cost him resources, that he will not then have for the fight to come and his minions would have no such advantage, so his CR 3 Megan would all be gibbering idiots in 3 turns.
Also, I'm not sure how the true seeing and illusory reality interact, if it's "real" for that 1 minute, do you still see through it? If not, illusory reality costs 1 bonus action/minute, so the only barrier to keeping things "real" non-stop is the need to sleep, and all that's without malleable illusion shenanigans or doing things like saying:
"within this space is a constant ear-splitting wail the smell of rotting flesh and the feeling of sand being constantly blown in your face...good luck sleeping"