I'd love for the cut to be smaller, but it is absolutely not a "death sentence." With traditional consoles (Nintendo, Sony, Microsoft consoles, and those before them), the barrier to entry is very high. If you are an indie, it is practically necessary to work with a publisher to get on those platforms. The publishers demand their own cut (in addition to Nintendo/Sony/Microsoft), and as they are running a business, they only take on games that they expect will make a profit. In that environment, weird little developers making weird little games will almost always be shut down before they can even see the light of day. I think it is a little easier in the modern day (you don't need a blessed dev kit to make a console game, for example), but I think the barrier is still not trivial.
The PC games space has always been more open. If you had a weird game you wanted to share, you could share a disc with your friends or make it available on your website. But, again, if you wanted to make some decent money, you probably needed a marketing department and to have a boxed copy on store shelves (which, again, means working with a publisher). With a few exceptions, hardly anyone would ever find your game otherwise.
With modern-day Steam, an indie dev needs only to pay $100 to put a game on Steam (and I believe that $100 is refunded if the game crosses a certain threshold of sales). Discoverability is still a challenge, but just by existing on Steam, an indie game has a chance to make a bit of money. Steam itself has some discoverability features that can boost the visibility of even quirky little titles. The indie dev needs to do their own work, of course, to get visibility, but they don't need to have major resources behind them to get that visibility. They don't necessarily even need to host a website anymore - the game has a page on the Internet through Steam after all. The indie dev can direct anyone who will listen to them to go there.
All that said, I do agree that Steam is practically a monopoly. If Steam decided they hate you for some reason, then that's it. You almost certainly do not have a viable path forward for selling your PC game simply because they have such dominance (see the recent controversy where major payment processors suddenly decided they would not facilitate the sale of lewd games, and Steam reacted by pulling any game that seemed to fall into that category. Although, even in that case, the harmful monopoly tactics are coming from different actors in a different industry). For the time being, I just think they are kind of a benevolent dictator.