From the history only ponzis are profitable in short holding and all other real potential based opportunities are proven to provide big returns in long term holding hence digital assets cannot be an exception here.
Yes; in my opinion as well, not just digital assets but each and every investment will be highly profitable in long run give that its fundamental are good in long run (and practically without stronger fundamental, you cannot expect an entity to be sustaining everywhere). So, if we want handsome returns from an asset then we should give it enough time.
Normally, investments take time before profit comes. It is not something that you just invest immediately and start expecting profit. This is the reason why a lot of people do fall for scam, because scammers will promise them that they would be making huge percentage in a week or even a day, and they would believe it and fall for it because of their greediness.
For the case of legit investments, slow and steady is always true and applicable; hence what OP is empathizing on this topic is fully acceptable for me.