Investing full-time requires you to devote most of your time and energy to analyzing markets and trading. Moreover, the price fluctuation of Bitcoin is unstable, and there is no guarantee that it will always be profitable.
I agree with your opinion and indeed if we rely on income from investing in crypto then we will definitely continue to analyze price movements and so on.
and I personally think that continuing to invest in btc would be suitable as a side business because the price of btc is very unpredictable.
but you can also invest in btc and make it your main income if you are really good at analyzing and your knowledge about crypto is very broad or for example it is very difficult for you to get another job, so in my opinion you can make investment in crypto your main income.