Cryptocrrency is a brand new interesting fintech solution, so I think that it's useful to have some crypto. As for investments, I think that the best investment strategy in crypto is long-term hodling. Prices fluctuate heavily, so it's quite hard to get some profit out of short-term trading.
Long term holding is good for BTC investment but for cryptocurrency as a whole, I don't think it is a one solution fits all since there are lots of cryptocurrency that are now dead and worthless. If we apply your suggestion then most probably many have lost huge amount of capital by doing long-term holding in these kinds of cryptocurrency. It is best to identify first the kind of cryptocurrency we are investing to avoid losses.
Cryptotrading is actually a gambling, however cryptohodling is indeed a good decision.
I disagree, crypto trading in its own term is not a gambling. It only became a gamble when the person do not know what he is doing, actually if a person don't know what he is doing, it is not called trading but gambling.
As for usage of crypto instead of money, I suppose that adoption level won't be so high that we will be able to use crypto for any purchase we want (there is still lack of overall mining power), so the only purpose of crypto is the asset of long-term hodling...
It is true that real life use case of cryptocurrency is still limited but I disagree that it is due to lack of mining power. It is due to lack of merchant adoption.