Every time I see a post with this specific claim, targeted at Valve, i just can't help but laugh.
Yes. They take a cut.
Yes. Everyone else takes the same cut, so you're biased, if you don't understand this.
Yes. They are an undisputed leader in the market, but no, that's not called a monopoly.
The difference is that Valve, while taking this cut, and being as big as they are, are consistently investing that money into improvement of the platform, AND also paying people to directly contribute to OSS, that affects everyone else in the market too.
Not to even mention the regular, very considerable discounts, practically platform-wide. Show me a time when Nintendo have done the same. A 10 year old copy of MK8 is still 50$
This isn't even a bogus claim, but just a waste of everyone's time