Interesting thread. Thank you for posting.

I think if I were to rate airports personally, I would have a more generalized system without percentages but more with a ranking type of rating. It would go something like this:

Convenience
Reliability
Attractiveness

For me, ease of transit and getting to/from the airport are first rank factors, so I would rate both under Convenience.

General on-time performance, for me, has something to do with the carriers serving the airport, weather affecting operations, traffic congestion on the ground as well as in the air, etc. All of these factors would go under Reliability.

Finally, I would ask myself questions, such as: does the airport offer a wide range of amenities? Is there a tourist information desk available? Is immigration and security a problem at the airport? Is the airport a great place to wait in? All of these factors I would group under a general factor called Attractiveness.