Without going into the motivations for building a startup and doing Y Combinator, I do agree with many of your points.

People can use Unity to build games and non-games. I personally don't think it fits a lot of different use-cases or application models and that it tends to be most successful in specific gaming verticals, but if it works well for you, by all means use it!

I'm strategically betting both on the lines between what is viewed as a game and not blurring, as well as developers needing a friendlier, more flexible way of building this kind of interactive content. I'm by no means under the illusion that strategic mistakes won't be made, or that this won't be a 10-year+ journey - realistically many (most?) successful companies have a very nonlinear path, including Unity themselves.