i dont think libra will destroy bitcoin as we can see now libra is the reason why the price pumping and i think no cryptocurrency will ever destroy bitcoin as it is more popular and more often used in crpyto world and one of the reason why many cryptocurrency is popping anywhere
I agree with you 100% in the part that libra won't affect i believe at all.
But also the coins popping everywhere is because anyone can do it, it will probably bring profit to the team who created it and also some do it because of ideals primarily but at the end they are not really needed.
After a lot of years passes by you will notice that they were truly irrelevant. You just have to notice the patterns.