Doesn’t this line of debate get kind of predictable?

It does, but that's an interesting psychological effect all by itself, where if someone keeps hearing the same -- valid! -- point over and over again, they start to discount its value.

Richard Feynman called it "normalization of deviance", but there's other names for it as well depending on the details.

I'm sure everyone has heard some variation of this before, especially in the work place.

I once got angrily shouted at by a customer because I turned up as a consultant and apparently I told them exactly what the last five consultants had said!

Well, yes, of course. It's the solution to their problem.

I regularly face variants of this at work.

"Yeah, yeah, backups are important, stop talking about it already."

"Yes, but they're still not happening and they still remain the top priority and it is madness to start a project to reformat the SAN array until backups are working!"

"That's what you said last week! You always say that!"

Etc...

There's a point where people lean into it and become purposefully contrary, making their refusal to change their opinion a permanent part of their identity as a person.