[jacknews]

I would ignore the tech stack.

Look at the quality of the people and your place among them. An increase in responsibility is a step up, but moving to a stronger team might be even more so.

[greatpostman]

I say the opposite, strong entrenched teams are hard to get good work from. Op will get the tech scraps and learn nothing

[jacknews]

By 'strong team' I mean a more highly-skilled team, not necessarily a more close-knit team. You don't grow your abilities from a stack (you just learn the new stack), but from people.