Even though I have edited this answer to take into account the OPs edits. I still find myself puzzled at the choice of the word degeneration. Bringing together the various aspects of different (and sometimes incompatible) APIs forms a large part of what software developers do. If on the other hand your question is to ask how to avoid getting yourself shoe-horned into a role that you feel is limiting your options to find other work, then perhaps either the parameters you have defined are too narrow, or the view of your role is itself also too narrow. I myself have worked on projects where I was responsible for specific specialist tasks without ever needing to work beyond those "limits", and I have never felt that these jobs were limiting in any way, as I could use them as examples in order to up-sell my skills to the next employer, with appropriate anecdotes about the lessons learned, and the skills earned.
Having myself interviewed many people over the years, I don't see signs that people degenerate into certain aspects of a role. I do see that people sometimes specialize, and that sometimes the specialization is presented as a limitation. This to me is a warning sign that the candidate is not very open minded, and likely doesn't really understand the development process as a whole, or hasn't the capacity to push beyond the roles that the candidate feels safe and comfortable in.
I would find any employer who saw the sort of work that I have done as a degeneration would themselves be likely to have a very narrow view of the capabilities of a good software developer. Software development is more than just being able to code for new GUIs or APIs, and a good software developer knows that there really aren't many opportunities to work on new projects, and that it is rare that you can walk into a new job and get to work on the exciting stuff, because you are generally being hired because there are a bunch of tasks that the established staff don't have the time to complete. Regardless, you will often find that "stiching APIs" together requires the implementation of new API layers to provide greater flexibility and compatibility between the existing layers being brought together. The real questions that should be asked of developers, is do they know how to manage and prioritize their tasks, or how to choose an appropriate methodology for testing and implementation, and whether they understand which tools/technologies to apply in order to achieve outcomes which deliver value to the customer. Essentially asking them if they know HOW to write software, and also how to handle tasks that may not necessarily be as glamorous as they might have hoped.
So to answer what I believe your question really should be about, I don't see that there is anything to fear from finding yourself being directed into a particular aspect of software development, but that if you feel it isn't the appropriate career path for you, you have the option of either discussing options with your boss, or leaving for a different role. If you do leave, then you need to avoid glossing over the work you didn't like, and find a way to draw useful experiences from the work you did.