The fact that "most of them aren't going to last long" is not enough to deduce that any specific one of them is not going to last long. All things that are old were once new, and survived. Again, the implication does not go that way and cannot be used even as a rule of thumb. It does not hold.

If you tell your rock star friend to go back to school, you are helping him minimize risk. The chances are that he won't make it, but that's not a consequence of the Lindy effect. It's because surviving in the rocking world is difficult as it requires that people pick your music repeatedly over other available bands, which is the requirement for the Lindy effect to apply, not its consequence.

More importantly, if you tell every rocker to stop and go back to school because their chances of succeeding are low, you end up with no rock bands. Because all rock bands have to start out being new.

Believing that most new rockers won't become big is fine. Believing that any rocker that is new won't make it is wrong, in fact you can be certain that some will.