Yeah, if you’re playing casually, you can train pretty much any Uma, even if they don’t turn out that great. But if you’re playing competitively for the CMs, the pool of viable Umas gets really restricted because of Mile aptitude. If your Uma can’t run Mile races naturally, she’ll never be as strong as one who can, since you’d have to rely on Mile sparks, which makes getting the desired race aptitude to S much harder.
There’s also the issue of the runs being too long, and you can’t really afford to use cards without race bonus.
Oh, and then there’s the clock problem. As you probably know, if you lose a race in Trackblazer, you can retry by using a clock. And man, you’re going to burn through a ton of clocks if you’re training backline Umas (End Closers or Late Surgers), since they get blocked constantly, or if you don’t have Mile A aptitude. You can get away with Mile B, but you’ll burn a lot of clocks.
As a backliner main, it’s hell. I started Trackblazer with more than 650 clocks, and now I’m down to 390.
Trackblazer sucks.