I have never seen such a situation in my life, just wanted to ask: how common is it?
I was fortunate enough to start at one of the big four out of school and work on some cool projects. I eventually went to work at a few startups, where it was more about being a good plumber (similar to what you are doing) than being a good coder. Many of the junior engineers got burnt out by trying to build and create solutions (where do I make algorithms?!?) around these 3rd party systems but the truth is, that wasn't what the business needed. Since I had already had my fix for creating some complex software, I did okay. I probably stayed at certain startups too long but I did get better at knowing when to build vs buy and how to build+buy+glue.
What helped me develop that knowledge was actually spending years building so I knew the cost of design/implementation/support/extension.