> Junior engineers are missing out on lots of knowledge transfer

I have worked as an engineer for > 20 years, and I currently work at a company of several hundred people that has been remote-only since its founding before the pandemic. I have personally helped to onboard a junior engineer on my team, and it's gone just as well as the junior engineers I've helped onboard at previous (in-office) companies. You can't make blanket statements like this; it's all about the processes that have been set up to facilitate knowledge sharing, camaraderie, etc.