Personally, I don't think any deal of potential profits is gonna go well for the artist. Most of us who do both can say, even including concept stuff, the art just takes way more time. The hard part isn't the idea. Everyone has an idea. The hard part is butt in seat work.
Personally, I think a collab with profits on a wish only works if both people are excited about each other's work. If an artist is into working with a known writer, or two friends want to make a thing, that tends to work well.
If you have an idea, writing or art, and need to make it come true, you need to pay for it. Industry standard is tricky because most payment is for pencils, inks, or colors, not all three.
Even for a starting artist, they should ask at least 25 in my opinion. For anybody with a few years of experience, they should get at least 40. Most people take about 3-10 hours on a page. That means with 40 dollars a page, at best, they're getting a little over 13$ an hour for their work. At worst, they're getting 4$ and hour. That's absurd. I professional level artist would be getting closer to 100$ for that work in the industry, which would still... be below minimum wage.
For writers, I would lean to a 100-300$ a chapter, and then maybe talk about 2-10% per page for professional quality, but writers can't just slap up an art portfolio to show their skill. A writer would probably need a history of successful products, or at least a dang good script. You'll notice a lot of writers who snag artists start with popular novels.