I joined a big tech co and dove in to a huge unwieldy code base that had gone through the process you described above. I did a lot of reading of the code, and soon became the only one that understood it and could make big architectural changes.

But.. that is a dead-end job. There is no career path being the maintainer of a large legacy code-base. It was pretty good if you wanted to rest-and-vest, I could do whatever I wanted. But there were no great features, no demo's, no selling of the work. Even small changes were painful.

Moved to a different team where everything is new and building from scratch and suddenly opportunities open up.