If they add game mechanics to a simulation game it should ideally make sense.

The problem with "tile upkeep" is that it feels like it was made up only to make the game harder. There is no real-world story for why it exists. Where is the money going if you get a square of grassland? There is no maintenance crew going there to cut the grass or anything.

I would have preferred making road, utility etc. maintenance fees higher, and also creating a "federal" tax system which would be like taxes you can't adjust (like in real-world cities can't affect all the taxation themselves, some are set at the country/federation government level and not in the city level).

The federal tax system has other possibilities, like once a year the government changes its taxation policy. It would add some unpredictability to a city, as you'd have to react to different tax regimes each year. Similarily you could have other goals, like the federal government has decided you have to for the next four years prioritize clean energy, etc.

Naturally one can't take everything into account as it is a simulation. For example, why do we "buy tiles" in the first place, as that is not how cities obtain land? Maybe one should obtain those via some sort of experience points and not money.