If you're having some issues, I totally understand that. I'm an admittedly terrible tumbler. My shoulder and back aren't flexible, I'm tall and lanky (not to mention with a whole slew of knee and foot issues). Also, tumbling scares the bajezus out of me. Like really. But there is absolutely no excuse for not trying 100% to improve your skills. Even if you have to have a heavy spot every time, you keep doing it unless you have a medical reason why you can't tumble. For example last season we had a girl have back surgery so she couldn't tumble the whole year. So while we were tumbling she did push ups, planks, and hip flexers. Just giving up is never acceptable. In terms of college, I would say a really incredible flier might get taken without the tumbling (someones gotta do the basket in the back.) Especially at a UCA school where individual tumble passes don't matter so much. But it wouldn't be preferable.
But you bring up a great point: Are there people whose body types will not allow them to perform certain skills. People who "just aren't made" for tumbling. And coaches, would you ever tell a kid that? Because I think a gymnastics coach would tell a kid that. You just aren't made for this sport. Would you ever let a kid who had been trying and trying and just couldn't do it give up?