I've heard from friends and people I know who have content in that the cuts are quite nice. I work with a guy who made a very popular map and he just got his first cheque from valve, and it was quite substantial. If you could tune your quality level relative to the time required, and of course guarantee you get submissions selected consistently, you could turn it into a full time job. One guy I know is in contact with several self-made millionaires who made/make TF2 and/or DOTA2 UGC.
There's a higher skill requirement to making that content since you need to know how to model and texture at a high quality, but several AAA artists have been able to quit their jobs, work from home, and even roll Twitch streaming (as they make their content) in as a side income to their UGC sales cuts they get from Valve. You have to assume the profit potential on CS is much lower because it's not F2P, but with the numbers exploding and Valve admitting themselves that they constantly re-examine whether or not to convert CSGO to F2P, you'd best get in now if you want to make real money.
People like Corridium Studios (Asiimov series) might not ever have a submission chosen again - even now that he's collaborating with artists better than himself - because the quality bar has risen so high since the skin economy blew up after he and a bunch of other early investors got paid. Still, he gets paid every time someone opens a case containing a collection that drops one of his skins, and his skins are still desirable, so he's still making money today. He'll continue to make money from his submissions until people stop opening and getting his skins from those select cases, so he's set for a while.
None of this is absolute truth though. Some of it is pure speculation, other bits are second hand knowledge from people I work with or chat with in UGC communities.
I've taken a bit of a break since I'm busy with other side projects, but when I get back in, I'm planning on doing the shotgun approach. One pattern that tiles nicely, applied to every single gun. The guy who made the P250 Supernova does this, and he has more skins in the game that any other creator! This means he's probably earning the most money! I wish I remembered his username, but I can assure you he literally has hundreds, if not thousands of CSGO submissions. He puts out quality and quantity tuned to a very profitable opportunity cost, in my opinion. Stuff like the Hypebeast guns probably won't get chosen, so why put in 20+ hours on one gun when you can put in 1 hour on a pattern to apply to every gun in the game, release the set, and then have 2 to 3 in that set be selected? Hopefully you understand where I'm going with this argument.