In my opinion, that's a weird way to approach the problem. That is, "I know I want to work for myself, so is spending the time to learn Swift programming going to get me there?"
You (obviously) can start from there, but I will suggest that you're skipping a very important question, to wit:
"If I am going to be self-employed, what are the skills I'm going to need, in order to be successful?"
It is patently obvious that the tech stack is the least important part of the answer. There are self-employed accountants, lawyers, house cleaners gardeners, roofers, etc., and none of them need Swift or even web development to be successful. Since you're asking about Swift but offering other tech stacks as options, it sounds like you care less about the tools and more about the situation. Spend a week talking to successful self-employed people about their situations and what they find most important to their success. Buy someone lunch and ask about how they got their first independent gigs. (Here's a hint: there are very few people standing on street corners, shouting, "Hey! I need an iOS developer over here!")