The difference between itch and Steam is quite significant. Right now, the daily average of sales on Steam is 5 (although these last few days it has gotten lower, 2-4 per day), while on itch we get 0-1 donations per day, with some rare days getting 2 donations. During April, 22 people have donated on itch, which resulted in $175 gross revenue (itch lets people choose how much money they want to donate, so some people give less than the default value which is $9.99, and some give even more). On Steam, Pixelorama has sold 265 copies during August, resulting in $2400 gross revenue. Of course we will get less than that due to the 30% cut that Steam takes, and August was a good month because it was just after the Steam release, so from now on the amount of copies sold will become less and less (unless Pixelorama gains more popularity).
If Steam had a pay what you want model like itch has, we would probably see a lot less sales, so it's not very fair to compare the two, as people can get Pixelorama from itch either completely free, or by donating a small amount, but in Steam they have no choice but to pay. But in general Steam has more people, and it has tools like the discovery queue which can bring more traffic to your Steam page (once you have reached 10+ reviews), and that helps. Our Steam page currently has double the impressions than our itch.io page in the last 7 days, but weirdly enough it has less actual visits than our itch.io page. Could be that the two platforms are counting visits differently, Steam only counts unique visits, but I'm unsure how itch counts page visits.
If you want to publish an app on Steam, go for it, you will most likely see more revenue than on itch.io. Just keep in mind that you have to pay a $100 fee for every Steam page you publish, but you will get that back once you reach $1000 in revenue. And it might be a good idea to have a period where your Steam page is public and you lead people there to wishlist it, before actually launching it.