That's a good point. One of the places I worked hired a ton of juniors and placed them under "senior" team leads, but the leads were too few, not exactly all-stars, and code quality was all over the place. I tried to have a positive influence on some of the eager new hires, with varying success (mostly because I wasn't very senior either, just a little further along than they were).

Eventually the environment became frustrating enough that I had to move on. Great people, really friendly environment, and even a product I believed in, but it felt so bad to keep having to read through awful, giant, bug-ridden code reviews with the same old rookie mistakes. I only had enough influence within my own team to slow the rate of bad code entering master, but it still came alarmingly fast. I think nobody from my team is still at that company. I really hope management has turned it around since.