Okay. I'm going to put my experience with monetization on both sites under a read more since money can be kind of a sensitive topic haha.
So of the two sites, if you're looking for monetization then Webtoons is going to be your best bet.
However, even despite this, know you're taking a huge gamble. On Webtoons, either you inch your way up in subscribers slowly or you explode in popularity immediately. I don't really see anything in between these two, like usually comics with something like 100k subscribers got the majority of their subs in one huge burst. I haven't really seen any comics that steadily gain subs that reach super high numbers unless they're one of the OGs from like 2015/16.
At the same time, if your job is seriously only sometimes paying $200-400 then maybe it's worth the gamble if you really have confidence in having a marketable art style and the ability to make a story that is at least mildly interesting.
Webtoons has two forms of monetization:
*Ad revenue: 1k subs and 40k views per month will allow you to unlock this. They will then give you 50% of the ad revenue earned on your comic.
*Beta Creator Credit: Once you are opted into ad revenue, you'll automatically be put into this program. Every 100k views per month will get you $100.
Now here where it get's tricky. We have no idea how your comic is going to perform, I can make no promises, and neither can you. Webtoons will only push what they think will gain lots of views for them (they are a business, not a charity) so it's possible your comic could go completely ignored and never even pass the threshold for ad revenue. The only possible way you'd be able to find out is by actually doing it.
I was making, ehhh, $400-500 per month from WT when my comic was on discover (not counting my linked patreon). about $300-400 of that was from the beta creator credit program (300k~400k views per month), and I got about $100 of ad revenue monthly. So the numbers you want to achieve are possible, but you do need to be in the top like.... 1% of discover creators (considering there's like 100k comics on discover)
As for tapas, I don't think there's any way to monetize effectively without being premium. I've made a total of 20$ that I can't even withdraw because the withdrawal limit is 25$ LMAO, here is my comic on tapas if you want to look at the numbers for comparison.
Anyway, I don't want to say that gaining the kind of popularity to start monetizing on Webtoons at the level that you're being paid at for your job rn is luck-based, it absolutely isn't. Well drawn comics with thought-out storylines, clean formatting, and a consistent update schedule will always perform well... But there is a 3-5% element of luck that maybe your story just really does not click, or your style doesn't go over well and you don't perform as well as you expected. Banking on Webtoons/Webcomics for a salary is just really risky unless you land a premium/featured position.
Good luck!! ><