Your reasoning is pointless. Neither are really getting any benefit from the system, and a 20 weekly hours job paying a MINIMUM WAGE isn't enough to make a living by any means and it's not an option for a common worker someone must be desperate to accept such therms despite getting a higher paid working hour. Besides, when a company needs someone working only 20 hours a week they are very likely to just sign in a temporary contract, common in retail stores during christmas season
The ones who got permanent 20-30 weekly hours jobs are a minority in specific jobs that pay more, like for instance fireman. My uncle is a fireman and the nature of his job make him work for 26 hours a week if I'm not mistaken. Those jobs that pays above minimum wage don't really need to pay a higher working hour for a part-time worker than they do with a full-time worker
My reasoning that people shouldn't work extra for free, but should actually be paid for the hours they work? Sure, whatever, if you don't mind working 48 hours and only getting paid for 40 that's up to you. I personally would never accept that in a million years though. That's the kind of thing we'd go on strike over in Europe.
Part time minimum wage jobs aren't for making a living solely off of that. They're for either students, who can only work part time because they're busy with school still, or parents where one works full time but they'd like some extra money so the other one does a part time job while the kid's at school or something. Or I guess also for retired people who'd like a bit more money on top of their pensions, my grandparents kept working part time for a good few years after retirement in order to afford holidays and things.
Things are not so easy around here.
I know it must be hard to imagine but you either take it or you don't have a place to live or food to eat.
Strikes are hardly of any effect, I can't even be part of one myself because even as we have laws allowing them you are screwed if you do one nowdays.
I'm a public worker, which were the "class" responsible for most of the strikes we had in the country, the last one we had here in my city (2018) was met with a legal issue by the city hall treatening the people takining part of it, the people that fucking work on the city hall itself! And even as they were under their right by law, the city hall tried to screw its own workers regardless, lost it legally many months later, and... nothing happened, they paralized the strike with fear and that's it.
The laws here are made to make you have no choices, even if they exist in your favor the system is so slow and so bound to having the money to keep it up for years that most people just can't even defy it at all.
The last and only real nationwide strike we had here since I can remember was the truck drivers one very recently which resulted in the price of everything going up and never coming back instead, and it was a succesful strike.
You have no choice, you just work more and more and receive less and less and do what you can. What people learnt was to take advantage of someone else instead.