I think trading capital ultimately depends on the trader and how much they are willing to lose per trade. There are traders who can take a $10 or $20 trading accounts to the highs of $5000 - $10000. Anybody can do it if they know what they're doing. It's very much possible these days since you can trade crypto futures and even use leverages. Your patry $20 capital would be $200 when on a 10x leverage account.
Anyway, I'm not here to talk about leverage trading. The point I'm trying to drive home is that any trading capital should be fine as far as the trader is comfortable with it and knows what they're doing. But one thing is clear those, the more the capital, the more you're likely to profit per trade if it goes well - for instance, gaining 500% on an $10 account doesn't seem to be worth it considering you only get $40 as profit. Compare that with a $500 - $5000 trading account.
This has also been my position on an issue like this. It's not the size of a dog that matters but the fight in the dog. Anyone who isn't faithful (profitable) in the little they're given can't be profitable in the much that they're given. It's better to have good set skills for trading before venturing into trading than jumping into it because one thinks they've enough capital that can't be squandered. No matter how much one has, if the set skills for it isn't there one will still not be profitable. It then becoming a guess game or gambling and not trading.