I've already responded to this claim in these comments. For what you say to be true there would need to be a large market of senior developers waiting in the wings refusing to work until wages go up.

You're also assuming the growth in jobs has been steady and predictable which it hasn't a spoiler in demand runs the whole idea that we just need more juniors starting.

The problem is companies can't wait so they can bring in workers who pay taxes here and contribute to the economy or they can move there jobs over seas. I expect we'll be seeing a lot more of the latter going forward.