I believe the main difference between both categories is that investments are passive, so the person doesn't need to stay tuned all day long to make profit, while a bounty hunter will have to work on different tasks and social medias several hours of his day to get paid. Anyway, investments and bounty tasks involve risks of losing money for the people applying to them.
And this is the reason why I quit bounties starting from the old days of ICO. Just ain't worth consuming electricity over worthless work that I could somehow use it better for freelancing.
And you are right on your decision. Besides the costs of electricity of running your devices and using internet, which is also paid, your time spent also has a cost which has to be taken into consideration on the final calculation of an executed work to reach out the conclusion if it worths or not and if you are being fair to yourself or not as a worker. Personally I think it only worths to work for fixed payrates, so you know how long you are going to work and how much exactly you are going to get paid in the end.