That's why Cura is free, though. Everyone can use it, for free, with any printer they want.
OK, you might feel that way, but I don't think most people do. This is also a whole other issue than the day-to-day development workflow. It sounds like you have a problem with a for-profit enterprise backing an open-source project which is totally unrelated to CuraEngine development specifics. No one would disagree with you that such a company should have a conscience, but I think UM actually has a pretty great reputation in that regard. Largely because of, again, things like making our slicer open source and working with competitors' hardware.
That's true, and to be honest, I'm a fan of the development model you mentioned. But the point is that Git workflows don't magically change code quality. If starting a new project we might consider a different model. Some of the private internal UM repositories do use this model. But applying it to CuraEngine doesn't make the code better by default. Merging into a dev branch and then merging into master makes no difference if the review process was not good, nor will it address the fact that you have the idea that the whole architecture of the code is wrong.
Again, if you are concerned, there's two things you can do: Read and review pull requests to point out code which you feel is overly complicated, and secondly, start a refactor to simplify it. These actions are not at all dependent on the branching model used.
And if you feel that you don't want to contribute your time to the project in these ways (participating, contributing) because it doesn't fit your philosophy, that's fine too. But then to spend lots of time complaining why it doesn't suit you absolutely is "concern trolling."