Essentially, this hinges on whether demanding price parity with other platforms is anticompetitive... I think that's going to be a tough hill to climb, especially as they're only asking to not be undercut as a supplier. There's no requirement to sell exclusively through Steam, and Steam even allows developers to give Steam keys on other platforms, including with game bundles that have a total "value" well below Steam sale prices.

Like, I use Steam daily, and buy multiple games most months in game bundles, but in the last few years, I've only made a handful of purchases on Steam. One game and my Steam Deck Dock were my only Steam purchases this calendar year, and my Steam Deck OLED and two games were my only purchases last year, but in that time I added about 150 new games to my Steam library.