I'm disagreeing with this statement while liking the general direction and content of it!
"There was only so much I could do to improve my coding skills. Most blogs epousing techniques to write cleaner code, repeating yourself, not repeating yourself, etc. are micro-optimisations. Almost none of them would make me instantly impactful."
I do expect a Senior Software Engineer to be good in programming. Because mastering programming is, what you do due working with it every day. The basics should just be.
Doesn't matter how impactful those are. Your role is to sure look left and right, but the road you are on is becoming an expert in what you are doing.
And generally speaking about the Senior title: I think from reading it, he does look in the right directions and it could be that he is already there but for me, Seniority become a thing not after understanding all of that stuff but actually incorporating it in a way that it became second nature and honestly, it took me years and a handful of core experiences along the way. But who am i to determine his seniority through a blog? :)