Platform exclusives seem to be rare (outside of Nintendo). I have an xbox (which I'm told is the wrong console), but I can play nearly everything a PS5 can. Most major titles seem to be very cross platform (PC, Xbox, PS5, and sometimes Nintendo). If anything, they stagger release dates, not access.
Steam's market share has held relatively steady at 75%. And in fairness, it does not seem like Epic is trying at all to improve their product, so I'm not sure they're deserving of more right now. GoG continues to have ts cult following (I had never heard of it until recently, but now see references to it frequently).
And it seems to be easier to game on Linux (and even Mac) than in the past few years.
I have no way of verifying this, but Perplexity states that ~5% of Steam games are exclusives. Have they exerted monopolistic pressure on the market in other ways?