Space is much more thrilling and exciting. Yes, I'm serious.
Disneyland's Space Mountain is less thrilling, but a better attraction in my opinion. Disney World's Space Mountain was horrible pre-refurbishment. My expectations are that the surface level refurbishments will bring it back up to an E-Ticket status.
Now I'm not sure what your argument is on Space vs. Rock 'n' Roller Coaster, but I do agree that inversions are not necessary to make a coaster effective. They're almost gimmicky, and at some points can be used as a selling point while otherwise damaging a coaster. I think the inversions work in Rock 'n' Roller Coaster (except maybe the third one), but on attractions like the Hulk, it probably has 2-3 inversions too many, the ride would be better paced if it had other coaster elements instead of jumping from inversion to inversion. Similarly, California Screamin's loop also seems out of place, and it really doesn't flow with the rest of the attraction.
Hate to break it to you but CBJ and HOP are still considered e-tickets by Disney
How much internal discussion about those two attractions takes place? Hall of Presidents is in a different situation than Country Bears due to the recent refurbishment, but if they are still considered E-Tickets internally than the definition has softened significantly, or Disney labels an attraction at one grade level and then doesn't change it based on the change in guest perspective. I think the latter is more likely. My point has been that if the system was still used today, most new attractions would be classified as D/E tickets when they first open and then as the popularity waned, they would fall into their actual placement.
There are some attractions that seem to be E-tickets in everyone's eyes, but you'd be surprised by how many people disagree on one attraction vs. another. I think the majority of people on here would say that Tower of Terror is a no doubt E-Ticket, but then someone that can't (or won't experience) will argue that it's not a family friendly attraction so it can't be an E-Ticket. Similarly, those same people may say that Haunted Mansion is a no doubt E-Ticket, while thrill seekers would argue that it's missing the thrill element. Disney may still use the terms internally. When these grading systems leak out to the public as they did for the D-ticket Toy Story Mania, and E-ticket Ariel's Adventure it serves the purpose of setting expectations. That in itself can be dangerous, but as a D-ticket I was very impressed with Toy Story Mania. To assume that Ariel's Adventure will be a better attraction, I have to be excited.