Alice in Wonderland ride was a D Ticket. Then a C Ticket. Then a B Ticket.
The DL train was an E Ticket. Then a D Ticket, Then a C Ticket.
DL's Rainbow Ridge Mine Train was an E Ticket. Then a D Ticket. Then an E Ticket. Then a D Ticket.
DL's Keel Boats and the Treehouse was C, then B, then C, then B.
Astro Jets were B then C then D. They must have really plussed that ride!!
Point being is that Ticket Level has always been loosey-goosey and Disney sometimes used Ticket Level to manipulate crowds, thus making any hard-and-fast rules more subjective than objective.
If Imagineering has a list of which rides they consider E/D/C... then they're keeping that to themselves along with what criteria they're using, which most certainly can not sync 100% with the historical tickets since they fluctuated over time.
Without input from the Imagineers with their list or criteria, guests can only deduce their own rules from the historical tickets. From a guest's perspective and experience, an E-Ticket level was highly correlated with being so impressive that it always had a long wait time. So, it's no wonder a guest would consider TSM or FEA an E-Ticket.
Let's get serious, if we were still using the Ticket system, TSM and FEA would be E-Tickets in order to reduce the lines, just like how they're in a higher tier on the FP system, even though, in a vacuum, they may have only been created at the D level.