I think EA and Codemasters ran out of time to optimize rain racing for the 2025 game...especially for more casual racers who use traction control. This is frustrating, but I understand why this happened because this is a chaotic time for EA and Codemasters. They got bought by Saudi Arabia's Public Investment Fund last year and they have to deal with the omnishambles of the new regulations. There are rumors that the 2027 game is going to use a new game engine, so hopefully the rain racing gets better in the future.
If you use traction control like I do, I would continue to simulate races to protect your career progress. I also recommend taking a occasional break from career mode to custom races with heavy rain. If you turn off the racing line, it's a fun challenge. Because it's a custom race, it won't impact your career progress.