> But the entire thesis of the OPs comment is that we shouldn't be valuing staff based on any one specific technical skillset, but rather based on their broader software development skills and experience, because learning the ins and outs of any specific software stack is not itself that difficult given enough experience.

Exactly. Tech stacks are extremely transferrable, at least to an experienced developer.

Imagine hiring a painter. You want a green wall. You don't rule them out, or pay them 20% less, because the last wall they painted was pink.