Yes it makes it a little bit harder for my son. But still even that custom races are lacking qualifyings, 24h settings, and other stuff you can do in other games.
But to set the liveries and driver names and stuff is something some other games don't offer.
Still I would love if they improve the AI. It's always slowing down after a while, letting my son win. And at some tracks like LeMans or Nordschleife, some cars don't pit and destroy their whole race. Very bad at Nordschleife where all cars except the McLarens pit every lap, while the McLarens just every two laps, making it too easy and too predictable. You can let them start at the end they will still finish on top.
And that's the fixed version by an update a few months ago, where all other AI Cars except the McLaren, didn't pit and went without fuel. That was a mess. Still to easy and predictable.