Worked for many tier 1 investment banks in the techiest corners of each org and some cases felt like startups with all the shiny new toys everyone else was using vs the dark ages of customized software straight from the nineties or some other entirely-in-house-built abomination in other places.
You need to make sure you aren't replacing them so fast that the median experience level is dropping, but it's certainly the case that the average experience level of the incoming cohort is expected to be lower than the outgoing one.
You see it at institutions, hundreds of individual "low bus factor" risks spread throughout the organization. The company would survive, but it would be a tough time, and a terrible place to work, during a large knowledge exodus.