> leading to a future where there is no longer a path towards developing those senior skills.
That sounds like unintentional death spiral for a company. You don't have juniors, it is hard to get seniors, because nobody is training juniors. So when all the seniors eventually leave, company is left with tech stack which nobody understands and few people hired for maintenance are only able to perform specific rituals left from previous generation. This might work for a while due to momentum but after some time it will just implode under its own tech debt and one unexpected push - like nobody is making servers which our tech stack runs on a we need to migrate...
