"One thing I have noticed is that while the old hats (those hired some time before the pandemic) are as productive, or maybe even more productive while working remote, it's a struggle to bring in new people, especially more junior people."

My employer has always (started in 2007) been fully remote; we've never had office space ANYWHERE. It's a small team building a relatively niche product, and we're pretty successful, but what you say is true:

Getting new people up to speed is hard. And hiring "baby developers" is just not something we've done. All our hires are midcareer or later. I feel like a fresh dev needs the office environment to get traction early in their career, and we just can't provide that.