Calling all theme park-goers

The huge map of the Island of Misfit Attractions (i.e. a Disney park of proposed but never-built attractions, mixed with my own creations and updates of no longer extant classics) on my dining room table just collided in my head with the recent and potential fallout from the Mission:Space incident. I started wondering-should an E ticket attraction be an E ticket merely by virtue of the thrills involved? Pirates and Mansion are now referred to as E tickets, even though they were D tickets back in the day, by virtue of the level of their theming and "classic" status (which are thrilling in a different sort of way than, say, Matterhorn or Space Mountain). Is calling something E ticket now more of a designation of quality than a matter of physical intensity? Is it simply a short way of saying "must-see" regardless of the reason?

Is Mission:Space then an F ticket because it is the most physically intense ride they've ever built? Is F ticket even a valid designation given the historical definition of an E ticket? What's the difference between E and a theoretical F? The joke I heard about attractions that could be designated F tickets (most of which are apparently mouldering in the WDI archives) being "so good they'll kill you" isn't really funny anymore. But is it true? Does "so good" necessarily "directly competing with Busch Gardens and Six Flags", or can it (in this day and age of the "bigger is better" thrill ride) be "remember how fucking revolutionary Pirates was when we opened it? Like that"?

For that matter, what is the cut-off between any ticket levels? What's the ideal ratio of A:B:C:D:E:~F rides in a park? Does that ratio change based on the growing population of young adults and the shrinking national population of children, or is it based on Walt's ideal of "a place everyone in the family can enjoy together"? Do F tickets even have a place in a Disney park? Any park?