Why not give the artists themselves a certain grading, and then give them either pass/fail based on their usual work? Giving artists a certain rank will be the part you deliberate about, but each individual piece need not require so much input, just a comparison to their other work. This way, art need not be critiqued so fine-grained, it can be done more broad strokes. Additional feedback can be provided on a less-frequent basis and money can be dispensed more frequently.
lot of drawbacks here, but might be a way to give more precedence to graphics as a way to make money for new users. Start at the bottom, review art work every 2 weeks or so? maybe more? So at the bare minimum, perhaps, new users could e expected to make, say, $100,000 per graphic. And if it exceeds expectations set by that user, you can increase their rank.
After writing all this out, i hate it, but I'll leave it here for posterity and for the sake of discussion.
They already get 250k for a 1/5, but people don't want to shitpost their way to income, and I think that's where the system can fail sometimes, as the reward for outputting quality can end up being minimal in comparison.
Not sure how well your suggestion could be implemented but I'll leave that up to the graders to decide.