Yes. Also, unless you define seniority on a per-company level, derived from actual time spent in the company, then you'll have plenty of senior developers landing in the middle of a legacy codebase that's new to them.

(And then, there are projects you look at very briefly. Just a few days ago, I used Sourcetrail to explore a certain research CLI application. I mostly needed to know how it does a few particular things, and Sourcetrail was useful for finding my way around the exceedingly complex class graph quickly.)

There's no good tool out there for reading source code. Sourcetrail is a step forward that's useful for anyone.