None of us knows the nuances of OP's situation. Given the thoughtful writeup, I can only assume that this was the right move for the team and situation.

I'm guessing I'm not alone in seeing bits of myself & bits of mentors/coworkers I've worked with over the years in this post, and appreciating that there's a good deal of nuance away from the extreme. As someone who is like a cousin of "Jeff", it's a useful reminder to read the room (company, team, product, etc) and calibrate my contribution accordingly.

Sometimes the most productive contribution I can make is to be the hero/10x IC/etc; just doing the whole project, putting out the big fire, etc. A few past jobs in startups worked this way: the team was a handful of extremely capable people who managed large projects on their own, in a way that moved the business forward – a team of "Jeff"s, maybe, in a place and time where that was the right team. This can be a really fun, rewarding way to work. Going from that to a senior member of a more traditional team (with more traditional responsibilities: setting people up to be successful, teaching through code reviews & pairing, trying to figure out a long term roadmap that I myself will never implement) can be a pretty big letdown by comparison. It is also inevitable for successful companies/projects. Clinging to what makes me personally happy (being sole owner of something big, interesting, and important) is unsustainable and, to the extent that I'm successful, harmful to the team and business. I try to be mindful of this. Stepping back, delegating, mentoring, ceding a place in the spotlight aren't always personally satisfying, but they are what I need to do as a professional. In the original post here I read someone who didn't do that.