Monthly crypto earnings not just come from holding onto your assets. There are agreements, much like how yield farming works on certain exchanges or well known wallet companies. Holding with the sole aim of profiting from the asset's price increase depends on market volatility. You'll profit when the market is on an upswing (bullish), but during a bear market, it won't yield any returns, and your assets may decrease in value.

Crypto investment is very dangerous for people who are weak at hodling. Occasionally FUD occurs and emotions are influenced which will have a negative impact on crypto asset holders. Therefore, regardless of whether it is good or bad to hold crypto assets rather than fiat in a bank, the answer is relative, depending on the person doing it and their risk profile.