Inevitable, yes. Now what the timeframe is varies according to different factors. I've seen pics of show cars stored in climate controlled storage with paint failure.
I've never really seen any filling ability with Z5. It does darken the paint slightly and I prefer the look to Z2. it's still a good product. Wolfgang is nice if you want to try something different.
I was at the track a few years ago. There was a guy with a 65 or 66 Mustang. I looked and it was a K Code. The guy pulled the original engine and was enjoying the car.
Technically an AIO would be considered a finishing polish as well. Several of those are well regarded for standard paint. That would make more sense than a dedicated finishing polish in a lot of...
I just used this yesterday. Smells great. It leaves the seats a bit on the slippery side though. I wonder if Sal has licensed this to other companies to manufacture.