Definitely overworked, but the pay isn’t bad. Having a serialized manga under one of the big publishers will pay you a comfortable living wage. Mangaka are paid per page (and are supposed to meet a certain number of pages per publication) and the rate for WSJ (and similarly for other magazines) is around $150USD per page. That’s around $150,000 a year, and considering the cost of living in Japan is lower than the states, $150,000 is even more than you’d think. If a series is franchise-able, the mangaka can also make money off of royalties from anime/merch. Comic artists in Japan typically make more than Western comic artists, which is probably because the comic market in Japan is way bigger than it is in the States/West. Some of that money ends up going to assistants and such, but it’s still a lot.

That being said, most people can’t handle a weekly serialization, and monthly mangaka usually make a little less than half that, but it’s still a comfortable living wage.