PM and QA (like everyone else) want to get their job done. What is that job?How are perfect pixel mockups helping them achieve that? Can you help them achieve that in a way that fits your objective too? Those are questions you need answered to discover how far you can push. And as a designer, you have the most underestimated tool to do that: empathy.
And regarding new needs, don’t treat as exceptions. Treat them as additional needs that your design system must satisfy. If you think of your design system as a product, it becomes natural that the users’ needs and your understanding of them will evolve.
The hardest part of such a project is indeed relevance over time. Finding the sweet spot between keeping things consistent without being rigid.