I can't think of any particulars right now, but my feeling is that many of companies the 2000-era bubble would be sound and profitable today, they just got to the market too early. It's very hard to judge an idea in isolation; the key is how that idea is applied to the market under particular circumstances.

If a true bubble burst were to happen, it'd kill startups by percents, not by merit. Some investors will keep money for their portfolio companies, others will sit until the market hits bottom and they can get better deals. It'll kill everything and everyone, not just the bad companies.

Right after the 2007-2008 financial crisis credit was incredibly tight. Nobody was getting any. The same would happen after a tech bubble pop.

Companies that are still in the growth phase, and not profitable yet would find themselves in real trouble.

You could argue those startups aren't (yet) delivering real value, and I'm sure in large majority of cases that'd be true. But not in all cases.

Well, if you are company that delivers real value to other companies that dont, then you will be in trouble.