Wholeheartedly agree.

Personas are useful for developing a general character that you can refer to. But you still have to be able to say "Alice Robertson, who is a demand-gen marketer at $CUSTOMER, is a prime example of this persona and someone we should talk to during product research." If you can't speak to an actual human and validate your ideas, then you are at risk of creating a fake persona who sounds just plausible enough to convince you to make wrong decisions.

Definitely - but those are normally called "development partners" in B2B, right?

Those two personas were very helpful to me in my previous life as a technical marketer; they helped me learn when to leave a job. Any time a company I have worked for told me they're shifting emphasis from talking about our product with the actual users to talking about "solutions" for the buyers, I knew it was time to start sending out resumes because the product was about to stall and the work climate was about to get insufferable.