I don't think it can be a source of main income unless you're trained in daytrading and TA. And with that, even TA experts say that crypto doesn't follow TA.
That said, I think daytrading crypto is gambling.
Bitcoin can't be a main source of income, because you're either hodling or selling for profit that one time. It's more like an investment that realizes.
I would not be a good financial advisor if I told people to make bitcoin their main income. They need a steady stream of income daily to make ends meet -- and you can't force the crypto market to give you that. On some days you're forced to hodl, and on other days you're forced to sell (if you know without a doubt that things will go down).
That's true, besides, many people would actually want to keep the ball rolling with their investments with Bitcoin or altcoin, thus, you would more likely see people not encashing whatever they earn and just reinvest it in something that could multiply their asset. That's how this market goes now, using it simple as a currency to fund your needs on a monthly bases can be done through another means, which means that when you become a seasoned trader or investor, using it as a currency would be the weakest way you can use it for.