AI progress is so massively out pacing any rate of loss of senior developers though.

Just for a thought experiment lets say junior hiring actually goes to 0% starting today and there is no other route into software dev for example maybe it is illegal for anyone under 22 today going forward to work in dev. Maybe something like ~2-2.5% of the workforce retires each year? And lets just define senior as 10+ YOE so 75% of the current batch of ~40 year working timeline. For simplicity lets just say the other 25% don't ever become senior devs and in 10 years the total number of senior devs has reduced 33% due to retirements. ChatGPT public launch was less then 4 years ago! Look at the ludicrous progress in the timespan. Even if progress suddenly massively slows or hits a wall it is currently hard to fathom it not improving at a rate of 3% a year.

More realistically I think we just have no ability to predict wtf things will look like 10+ years out at this point which is the point in this artificially constrained timeline where a reduction of senior devs just due to time would even start to be noticeable I think.