I don't know about this... I think that the "expert" AIs on RTS games just get more resources (not compute resources, but in-game resources) so they can create more units. I'd love to play against an AI component that has the same resource collection speed as the human player.
I wonder how strong such an agent would be today if years ago AlphaStar was on par with pros. All those fun projects (the one with Dota 2) died out when LLMs took the scene and RL died out.
Yeah, cheating with resources or vision is disappointingly common. I remember the Green Tea AI for Starcraft 2 being pretty hard, but it looks like above "medium" it cheats (but the TL wiki does say "very easy", which will give you 10 minutes to set up, is equivalent to Blizzard's "harder").
I still remember the mod scene in original StarCraft (+ Brood War) - it got to the point of supplying alternative AI algorithms, and there were plenty of non-cheating ones that were a noticeable step up in difficulty. At that point I already played competitively with friends and on-line, so they were only very challenging to me; for a new player, or someone casually doing the single player campaign, or just me a year earlier, they'd be impossible to beat.