The way i've seen it is Junior/Senior as a label of wisdom/engineering acumen and experience (not just a title) is not directly correlated to years of experience. Some people just have the same year of experience/level repeated 3-5 years. Some "Junior" with 1 YoE can come away with learnings some seniors never get in their careers. Not wholly their own fault, but it's a fact.

I cannot grok this. Are you saying that “juniors with tons of experience are very common?”

Do you mean that there are seniors with a lack of experience? I believe yes I was also making that same point.

Ageism in the industry also encourages seniors to appear to be plugged in with the newest shiniest thing, so we kind of do it to ourselves with our hiring practices.

We need to divorce seniority from talent.