A good obvservable metric would be, when it maintains a stable price against bitcoin for lets say 5 years+. So for example, lets say BTC/Shitcoin is always around 0.0005 BTC +/-10%, if its able to maintain roughly that price long term I would say that it stopped being a shitcoin since it maintains the purchasing power, so even if you use it, then forget about it for a year, you still have the same purchasing power as holding btc. So far all of them are bleeding against bitcoin or oscilating (on a downward path) a bit. So even if the tech of the shitcoin is useful for something you need, people still just use it for that isolated purpuse and then move back to btc.

I think the main reason for none of them to achieve this is that we are still very early, most of the use is still speculative instead of real daily use... Some will technically always bleed if they have infinite inflation baked in.