Actually, I have addressed this before with little success, but, I still believe it. First off, there is no "E" category. That was something that was used to justify charging extra for the right to ride it. That was abandoned as soon as EPCOT showed up. No one except the guys that used to classify those attractions really new what criteria was used to determine what was an A or and E. It seemed to hinge more on popularity then quality. I guess that the law of averages would mean that some of the best attractions would have gotten the coveted "E" rating. Now that there is no "official" rating system for what constitutes that rating, we, the fan base, have taken it on ourselves to make that determination. A number of people place that rating on quality, length, fear factor and other things that they are pulling from the sky. There is no definition for "E" partially because they never identified them and also because it no longer exists except in the minds of some fans. I'm not one of them. If I were to use the original criteria of whatever the public wanted to see the most so we can charge more money for it, then I base it on popularity. Of course Splash Mtn. would have been an E along with BTMR, Space Mtn. and others at this point.
We must remember that the Tiki Room was once an E, along with Country Bears and Small World and others. Are they no longer quality or have they just dropped in popularity and therefore no longer considered E's by the self appointed experts? Personally based on my judgement 7DMT, Frozen, TSM are among the attractions that would today be considered E's. Are they the marvels that the old ones were? Actually, yes and they are popular too. If Disney were to decide tomorrow what would now be considered an E, you can bet your last dollar that those would be included in the extra money category.