If steam went public and had the usual revolving door of MBA CEOs keen to "maximize efficiencies", you can bet that Steam would turn just as malign as the adtech industry.
A private company is not a corporate raider.
A private founder-owner-CEO combination (like Steam) might be the least vulnerable organization to many of those ills, short of a cooperative (not sure it counts as private ownership).
The last game I bought that wasn't on steam was probably Kerbal Space Program, in ~2014, and later converted my key to Steam when the option presented itself.
*Epic offers 0% cut for the first year to most indie games
GoG exists too, and just like what happened with streaming services, gaming companies have pushed out their own shitty platforms full of DRM and spying. Steam is still #1 though.