Zero interest rates kept many weak companies alive but they also have give great companies time to find product market fit, and the hard part is to separate the two in hind sight
I'd be interested in any examples where a "zombie" company in the US was sloshing around for a few years and then finally found product market fit. I think it's probably incredibly rare, and I don't think it's really that hard to identify weak companies that have been treading water for years as you appear to think.