So the % is debatable of course. There's cases where an AI agent can save weeks worth of investigation, there's cases where you are mainly blocked due to processes, and many different circumstances. It's up to every company on their own to decide it. But if they decide it's 50%, why shouldn't they spend 50% of salary on it?
Like imagine a large company with thousands of microservices. You need to build a feature, before you had to setup cross timezone team meetings to figure out who owns what, what is happening in each microservice, how it all connects together. But now you can essentially send an AI Agent to scour and prepare all this material for you, which theoretically in this planning could save hours of back and forth meetings.
If 1 hour / 1 eng costs $200, then a 10 people 1h meeting avoided would save $200 x 10 = $2000 alone.
I don't see it as a replacement for dev, it's more of a multiplier.