Valve is certainly better than others, but they do prevent publishers from selling their game for less outside of Steam (if they sell that game on Steam), and I think that is anti-consumer.
That's not correct from what I've read. You are more than welcome to ask for a source instead of accusing me of falsehoods.
"To help maintain its monopoly power, Valve uses what is known as a Platform Most Favored Nations (“PMFN”) clause in its agreements with game publishers which prevents game publishers from selling their games on other on-line gaming sites with lower costs, fees, and/or sales commissions for less than the game publishers sell their games on the Steam platform"
https://www.masonllp.com/case/valve-mass-arbitration/#:~:tex...
Nothing about that refers to Steam Keys. I did do some cursory searching to find sources which disagreed with this interpretation but was unable to find any. There's always the possibility that the class action lawsuit was misguided or incorrect- so if you have any sources that say otherwise, please provide!
..Or I suppose, some examples of games that sell for less (excluding temporary sales) on other stores than they do within Steam.
EDIT: Elsewhere someone provided this Ars Technica article where an unidentified source at Valve said this does only apply to Steam keys, which is likely what you are referring to: https://arstechnica.com/gaming/2021/05/why-lower-platform-fe...
So it's definitely a contested fact.