It doesn’t matter what a Dev said a long time ago

It matters, because that is an explanation to how it works. This (what I explained) explains it well. If you choose to ignore the logic, then all your argumentation makes no sense. Because you ignore what the verification actually means.

They advertise that a steam deck verified game “performs well on the Steam deck”.

Which is inline with what I said. It does not contradict to what the developer said.

I know well is a broad term, but anything less than solid 30FPS should be immediately “Playable”.

I strongly disagree. First it depends on what game. For a fighting game like Street Fighter or Tekken where all versions of the game MUST be 60 FPS to be on the same playing field, I can understand that 30 FPS leads to just a "Playable" rating. But if we talk about a strategy game like Civilization where FPS is not that important, or maybe a JRPG like Final Fantasy, a 30 FPS should not lead to just being Playable rating. That would be wrong.

Games like Final Fantasy 16 that frequently dip to 15 FPS cannot be marked as Verified.

Just because it sometimes goes below the mark does not disqualify the Verified rating. As explained in my previous reply. I think many (including you) misunderstand the Verification system with a Quality or Performance system. If the game however is constantly below 30 FPS and the FPS is crucial for the game, then I would understand it. But dipping here and there does not disqualify in my opinion. I think Valve handles the verification correctly.