That's a whole lot of assumptions in that OP.
In any case, the industry would have done fine without any of the big 3 after the market crash. Especially these days when many other tech or software giants could step in. Or that MS so closely mirrors Sony anyway, that if they stepped aside I think there'd be a lot of rollover without much hassle I'd imagine.
Each and every one of the big 3 also supports and funds unique games of their own as well, ether through partnerships of studios that are close, or third party.
With all that being said, the main reason I was interested in console games was mid-tier games, Japanese games and party games with lots of people and something new to offer me that I can't get elsewhere. Most of that seems gone now with previous generation and especially this one.
If I want power(or the same gameplay with better graphics) and standard controllers I'll stick with PC. Since it's something I need and would have to upgrade either way, and what i can't play today, I'll be able to play it at 4k tomorrow.
Also I'm not exactly sure where people got this idea that Sony made videogames consoles into more than a toy, when Sega was already moving in that direction anyway. It was an inevitable evolution imo, especially with your biggest competitor's selling point being that it is a toy. A contrast in marketing and software would have eventually happened.