But XP do not level up linear. Usually you will need more and more XP to level up, or in a car game, you get more credits to buy new parts or new cars.
I don’t think I had an issue where Wreckfest got trivial because, I earned more credits for harder difficulty.
The devs really did a good job in balancing it. Also Infested Planet did it that way. Of course it is more work on the dev side.
Agent of Mayhem can get really nasty in a mission on a high difficulty, but if I know that it is worth it for the XP and money, I will try it and leave my comfort zone. It did not make the rest of the game trivial.