Indeed it is not. Games tend to have a limited budget. If you spend too highly on one particular aspect, the rest suffers, since you can only allocate so much money to each team/project.
In my opinion, if AoE4 graphics look about as good as AoE2 DE or 3 DE, most people probably won’t complain. I wouldn’t. Just give me a fun game to play. RTS players on average tend to be less fussy about graphics than other gamers (otherwise, why would a 20 year old game still be popular in the first place ?) I get why an RPG wants to have graphics as good as possible, but I think for an RTS, going above and beyond has very little return for investment.
I’m not saying that graphics should be made intentionally bad or something, but I just don’t mind if it’s not going to be anything flashy. I’ve seen too many games that have amazing graphics and otherwise full of bugs and bad gameplay experience.
Making a balanced and fun game is actually not that easy. Coming up with numbers is really an art in itself, and requires quite a lot of testing and experimenting. I’d much rather see them put effort into making fun and balanced mechanics, exciting and fun campagins, a decent selection of civilization (no one likes a dumbed down sequel for a game) and a game that generally isn’t oversimplified (selection of units, buildings, map sizes, map types should be varied)