You hire a junior dev at $x. Let’s say $75K. They stay for a couple of years and start out doing “negative work”. By the time they get useful and start asking for $100K, your HR department tells you that they can’t give them a 33% raise.
Your former junior dev then looks for another job that will pay them what they are asking for and the next company doesn’t have to waste time or risk getting an unproven dev.
While your company is hiring people with his same skill level at market price - ie “salary compression and inversion”.
First, that's not true. You need people to actually write code. If your organization is composed of seniors who are doing architecture planning, cross-team collaboration, etc - you will accomplish approximately nothing. A productive team needs both high level planning and strategy and low level implementation.
Second, the LLM engineer will be able to grow into other roles too. Maybe all of them.