The AI does indeed pay reduced mineral maintenance (and in some cases reduced energy maintenance). To my knowledge I have never claimed otherwise, only that the AI does not simply get free ships or otherwise can build for free (which it does and can not). The reason it gets reduced maintenance is mostly to do with the complexity of the tile system and the fact that it isn't as good as a player at resource prioritization. Hopefully at some point we can get the AI good enough to not need these sort of cheats, but the honest truth is that AI will probably always need to cheat in some specific ways to cover up weaknesses (another example of this would be that the AI pays much lower costs for gene-modding because otherwise it tends to hold up its own research for far too long).
I suggest you read the "Stellaris is Way too Unfair" thread, where you directly tell another forum goer that the AI doesn't get any resource buffs on normal, that it is simply better at managing its economy than the player in question.
The reality is that "paying less maintenance" is an economic buff. If you're paying 20% of your mineral income on your fleet, that's a substantial amount. Even more noticeable in the new update, but even pre-2.0 100 naked corvettes would have a maintenance of what 50 minerals a month?
Current game: My Rethellian Coalition has mineral expenditure on ships of 556 per month. 50% of that gives the equivalent AI next to me an extra 278 minerals per month to spend on stuff, including ships. That's huge.
You've been pretty rude to players on these forums about this issue. It would be lovely in future if you:
a) did not lie by omission,
b) did not deride players who suspect that the AI is cheating (because yes, free resources is cheating, it doesn't matter if its a console hack or a If(AI) then (0.5*Maintenance Cost)
c) were upfront and honest about the advantages the AI is getting, especially if players are saying "I suspect the AI is getting free resources"