And you're also neglecting the fact that you cant keep up with your investment for a long term when you dont have a stable source of income. The reason why a stable source of income is important is not because of the investment alone, its because of the necessary things you must do before thinking about investment. I believe you know them. Without a stable source of income, you can't have an emergency fund, savings, and funds to care for your basic needs, talk more of to have discretionary income. It might make you want to tamper your investment.
You really don't need a stable source of income to keep up with your investment for long, it depends on what age you got into bitcoin and the responsibilities on your shoulder within that period of time. Take for example a student who got into bitcoin at a time that he depends on parents for survival and he has some spare and wishes to invest it into bitcoin for as long as he remains a student and even upon graduation still gets periodic allowances from his parents while living with them to curtail expenses pending the time he secures a good job for himself and starts fending for himself. If this goes on for up to 5 years or more from the time he got into bitcoin as a student until he stands on his own, then you can agree with me that he has been investing into bitcoin for a long-term without having a steady source of income.
You may talk about building backup funds or emergency funds, such a person might not really need to build such since his parents or backup unit are there to respond if he has an emergency or has any pressing issue, so he can freely invest as much as possible while using his support unit as a backup option.