This is a real hard one to answer. I feel playability has nothing to do with it. It is pricing and pricing alone. Assuming machine has been shopped and is ready for plug and play.Otherwise there are too many variables.

My opinion is made on the basis that pinball machines are labelled A B or C because of the financial part only.

A List - relates to the top priced machines. The top $ bracket. example, Cactus, Monster Bash, Medieval Madness,Attack from Mars etc. These machines have shown on a regular basis that they attract and sell for very large amounts of money. $7,000 grand and above.

A minus list -machine that sell around the $5,000 to $7,000 mark - example Indianna Jones, Twilight Zone, Scared Stiff, Theatre Magic , Addams family etc.

B List - Machines that are very close to the $5000 mark - example, Star Trek next Generation, Junkyard, Guns n Roses, and so on.

C List -  Any machine worth $4 grand or less. too many too list.

I feel A B C listing really relates to money only, and has nothing to do if a machine is well liked by most or not.
Fishtales, Getaway and say Whitewater are all c list for pricing, but not many people would argue against them being A grade for playability.

You need to say "are we talking A list pricing , or are we talking A list playability", thats the way to get a  indication of the topic and keep it on track. Is it a price list or a playability list. there has to be two different lists to keep the topic in perspective.

I hope my version helped.