I think you have a skewed vision of “free” and “open source”. Yeah, sure, commercially viable projects pay royalty fees. But it’s a drop in the bucket and very affordable and friendly. The engine is huge and with every release, we can expect new bugs along with new features. On top of that, some things get more stable and old bugs get squashed. Anyone who has been a developer or even designer/artist that actually *uses *a given platform, tool, engine, SDK, or whatever, for any amount of time is familiar with this cycle. It’s the nature of the beast.
It seems you don’t know what Unreal Studio is? It’s targeted at enterprise markets. Straight from the page: “Create stunning real-time visuals for architecture, product design and manufacturing. Unreal Studio drastically reduces iteration time through efficient transfer of CAD and 3ds Max data into Unreal Engine”. So, feel free to pay for that or whatever. It’s not going to change a whole lot, unless you are in the ArchViz, ProdViz, or similar markets. And if you were at that level in those industries, you would likely not be illogically grumbling, because you would be quite used to buggy tools 
I have to agree that your opinion on DoF was a bit unfounded. A lot of games use it, some badly, some quite well. With all the cinematic stuff being done with UE, a faster and higher quality DoF is a welcome addition. Along with all the other lovely bits. Don’t like it? Don’t use it. Just because a team of hundreds along with a community of thousands that also contribute are adding new features, doesn’t mean bugs aren’t being fixed. Some fixes get pushed back, others shuffled around. Again, it’s part of the scene. There are tons of us annoyed with bugs. It’s okay though- they eventually get fixed, because Epic and the community that has access to the source are awesome like that.