if you believe the social blade website, it's not much, it's all the sponsorships/merch like you said that bring $. JOB is also by far the biggest.i dont think these guys are even making decent money purely off youtube in the first place. i got word of what JOB makes off the channel and he got the most subs in surfing. its not enough. he basically pays his filmers with iot and thats it. someone like Gravy, and especially Zeke are making McDonalds money
they making most of their cash of merch and endorsements.
I've watched videos by youtubers on how much youtubers make from youtuve itself saying it's anywhere from 1k to 20k per million views. that roughly lines up with the social blade