A 15–20% fee would be much fairer in my opinion. They’d still be making plenty of money while letting developers keep more of what they earn through their hard work. At the very least, they should differentiate between big players and smaller indie developers.
Taking a larger cut from big players would incentivise them to make them create their own marketplace, where they exclusively publish their own games. Then we're back to square one.
Honestly, I think 15-20% is doable, if they make money in other ways. CS skins, new game releases from inhouse, etc.
A 15–20% fee would be much fairer in my opinion. They’d still be making plenty of money while letting developers keep more of what they earn through their hard work. At the very least, they should differentiate between big players and smaller indie developers.