You can be a senior, very experienced developer using a particular tech stack without all of that experience being developed with that tech stack.
In fact, I'd say at a senior level a developer should have considerable breadth of experience and the ability to comparatively evaluate tech stacks, not just skill in using a particular tech stack.
In fact, I'd say at a senior level a developer should have considerable breadth of experience and the ability to comparatively evaluate tech stacks, not just skill in using a particular tech stack.