I like working with people who get the job done, quickly and simply, and focus on functional completeness and minimizing defects. People who I can count on to tell them "here's what it needs to do" and I can know that I'll get something out that does what we need.
I don't like working with people who obsess about every line of code they produce and who worry more about documenting things internally than about getting working code out the door.
Sure, given the choice I prefer clean, maintainable code to shitty, sloppy code. But complaining about diagram quality in internal documentation? Unless you are making components for NASA or MRI machines, I think you're obsessing about things that don't matter that much.
The reason the guy in question is senior to you is because management likes people they can count on to get shit done.