I could release mysmellyarsecoin tomorrow, print 20 million tokens, hype the shit out of it and put ten up for sale. Hey presto, I've just taken 10% of Bitcoin's market cap.

The coins that have taken Bitcoin's market cap have precisely zero use. That's when they're not forking all over the place.

The main use for all of it is still speculation by a long, long way. Bitcoin is the only one with a sliver of utility. Once that sliver grows, and there really isn't anything else with any utility, then the speculation will recede.

People can of course reward utility to other coins easily enough. There isn't any reason Doge couldn't do just as good a job, but comes a time when people have to settle on what they're going to reward value to otherwise it all turns to dust.

That's still Bitcoin and every day that it remains Bitcoin makes it stronger.