Ticket levels, when there were tickets, were quite... fluid at times. The Ticket level reflected the price per ride of the attraction. Attractions that cost more to build, had a higher price to ride, and thus, a higher ticket level. But, Disney also used the Ticket level to move crowds around. Attractions with long lines, even if they weren't expensive to build or maintain rides, had their ticket level bumped up to discourage long queues. And conversely, rides that lost their long queues had their ticket level (and thus, cost to ride) dropped to attract more guests.
When things went Pay-One-Price, ticket level should have become meaningless, but it was kept alive by two groups that had two different criteria: Imagineers and Guests.
For Imagineers, who still use "E-Ticket" internally, an E-Ticket ride is one that has cutting edge tech and gags and price-tag and fully themed. Obviously, what was once cutting edge may no longer be considered such as time goes by, but it's still a historical E-Ticket.
For Guests, any wildly popular ride that gets long lines because it's wildly popular gets called an E-Ticket.
If Ratatouille was once considered by Imagineers as an E-Ticket when it was being built because LPS rides were cutting edge and it was fully themed, then it's an E-Ticket, even if Guest appraisal would downgrade it to a D-Ticket when they compare it to brand new LPSs, like RotR.
Whether Imagineering actually called Rat an "E-Ticket" internally... I don't know.
But some rando guest's appraisal of how much they like the ride... is not the industry's determinant of whether the ride is actually an E-Ticket or not.
