The post-ticket-book application of ticket designations is odd. If you don't like how an attraction is shaping up, just state your opinion. Don't try to give your opinion a veneer of objectivity by making up a letter.
We have no idea what letter this, or any other post-Eisner ride would have if it had a ticket, and we never will. The ticket system was intended to manage crowds, and was never an absolute yardstick of quality, ride length, cost, or anything else except for the ratio of supply and demand. At Disneyland, you once had to part with an E-Ticket to ride a mule. Would you call that an E-Ticket attraction now?
But let's say the Snow White coaster really "is" a B-Ticket. What else was a B-Ticket? The Casey Jr. Circus train. Why is a B-Ticket family coaster going in Fantasyland a cause for mourning?