Steam is a terrible example for this. First of all, Steam isn't a company, it's a product. Valve is the company. Second of all, unlike the App Store or other similar infrastructure, it's not like you're locked into Steam, so they're not really rent-seeking. Steam has had plenty of competitors over the years(Direct2Drive, Games for Windows Live, that garbage GameStop store), they all sucked, and as far as I know there's nothing stopping me from publishing on multiple stores & ignoring Steam. Third, Valve hasn't exactly been doing nothing - they've done more than any other company to the gaming experience under Linux & have pioneered VR. Odds are good they wouldn't have taken those risks had it not been subsidized with comfortable margins they got from Steam.
If you had cited, say, the App Store, or something that has actual monopoly power in terms of infrastructure (like our good friends at Comcast) it would have been a much stronger argument.