From the opinion piece:
Last year, I pointed out how many big publishers came crawlin’ back to Steam after trying their own things: EA, Activision, Microsoft. This year, for the first time ever, two Blizzard games released on Steam: Overwatch and Diablo 4.
Steam gets something to the tune of 30 % as their fee.
30% is industry standard from Apple, Microsoft, Google, Sony, etc.
Steam taking 30% is nothing out of the norm