The reason I'm pro Unity is because I get a lot of resources for free - not only from Unity, but also from an awesome community. Because of the size of the community, you can generally get help. I struggle with software that have small communities to get (a) the developers to take my bug reports seriously (b) help, when I don't know how to do something.
If you're making a lot of money from your game i.e. $200,000 you'd likely upgrade to Unity Pro or Enterprise. At that point the cost per install in your scenario becomes 1c or 2c.
In the meantime, those of us earning a few cents per game can create games in robust software for free.
I agree their argument is weak, but I'm ignoring that, and looking at the bigger picture. They need to make money to stay in business. And they increased the minimum earnings before you need to start paying from $100,000 to $200,000 per year. They have to make up that shortfall somehow.
From my perspective, if my game was making that kind of money, I wouldn't begrudge Unity the money because they take the risk. They say: "okay, you use the software for free and we'll carry the costs of your game development - which is considerable when you start looking at the analytics, UDP, etc. they give me for free. If you're successful, we want to share in that success, so pay us a fee then, but we'll cap our fee or reduce our rate as you grow and use more of our services."