There are a lot of capitalist countries that haven't collapsed yet. We'll need longer than our lifetimes to see proof that it can never work.

It's more that it's unsustainable. Collapse can be delayed, but not outright prevented as long as the Tendency for the Rate of Profit to Fall exists.

But I suspect that people in power just aren't good enough to keep it from going bad eventually.

It's already "bad," just constantly decaying.