For a while i have eyed toward TF2 as i fundamentaly like this type of game but as former Transport Tycoon player i miss a little AI competition and as far as i am concerned i only found that the Devs do not want to add that.

Is there any mod out that adds meaningful AI competitors or is this game still sandobx mode only?

No competitors available, but the game is great!
Very relaxing and creative.
You fight the budget, at least in the beginning, then the money starts pouring in...
If you are to play it at 4k you need a beefy gfx-card though, like RTX 40-series...if you want 30+ fps anyway.