But all this begs the question as to why a PF that is painted and then cleared holds up well, but for some reason its not applicable for a ramp?

2 pac clear is bloody hard wearing stuff.. so is 1K for that

because wood is more poorous than metal, the bond on the play field is better than it would be over clearing over a smooth chrome surface.
i think plating is the only answer in this case. the original was just done poorly.
plating would also be the cheapest option also, and the best.