>if company uses a very well tech stack, development and rewrites will be faster due to AI having way more examples to draw from.

Eh maybe not.

Stuff that has a lot of deprecated features is honestly burdensome on AI. It keeps rediscovering the deprecated features as the understanding that they are deprecated fall outside of the context window.

What you need is something that either never deprecates syntax, or is <10 years old with minimal changes over that time.