I think you underestimate how many altcoins exist.

A few days ago I saw an interesting article by CoinGecko where they show all altcoins that have died in the last years. The number was over 13,000. So these can already be classified as "failed experiments". This number is from January 2024 however, so the real number may be a bit higher.

CoinGecko has currently listed 16,100 coins approximately. Thus there are about 30.000 in total in existence with at least some minimum relevancy (i.e. CoinGecko considered them worthy to list, or have paid to be listed ...), but 13000 of them are of such bad quality that they are not listed anymore. And there are probably much more that were never listed at CoinGecko. CoinMarketCap even lists 2,4 million (!) different coins.

Taking the more conservative CoinGecko number: From the currently 16,100 "listed" coins, being honest, who's talking about >15,500 of them? Okay, at least 3000 are memecoins (I don't know if Coingecko's category system covers all coins), so somebody is perhaps talking about some of them for some time (1 per 15 minutes, perhaps). But we have for example almost 650 "Smart Contract Platforms". We normally talk about 10 of them as a maximum. The rest (98%) could be also classified as "failed experiments" because nobody is using them.

In general I think that of the existing altcoins, at most 500 or 1000 have some value or are doing something interesting. That's 2-3% of all those which were listed at CoinGecko and less than 0,001% of those listed at CoinMarketCap. Perhaps the number HideYourKeys is talking about is "only" 97%, but not much lower