It seems OPs opinion is heavily influenced by their personal experience, and it doesn't generalize well. In fact I have the complete opposite opinion on several points
> Your words have weight. If you, an IC, say "guys, we really should write tests", everybody goes "oh, crazy old Vladimir, all grumpy again, haha, where do you see tests fit here?". If you, an EM, casually say "guys, we really should write tests", you might be surprised to find the tests unexpectedly growing in different places.
I can't generalize, but in my company engineers trust Staff engineers way more than managers. Everyone has informal authority, and from my experience engineers tend to respect other engineers more. As a manager you can ask people to do things, but there is no guarantee they'll do it. And if you need to resort to your formal authority to resolve something, things probably went wrong somewhere.
> Frankly, after 4–5 years of working in a particular tech area, you can solve the vast majority of practical problems well enough.
If this is the case, then you are certainly not pushing yourself hard enough. Maybe it's company specific, but right now in my team there is a neverending list of ever increasingly bigger and more complex problems. The idea that you can master everything in 5 years sounds extremely naive to me.
> Life of an engineer is relatively relaxed. If you don't have anything urgent, you can go lay on the grass for half a day
Please OP tell me where you work. I'd like to lay in the grass half a day, rather than being constantly pulled into 10 different directions and having to push back on new requests.