Regarding HWE: Yes, absolutely. Take note, Larson: this is how you write an episode in conjunction with a holiday (he wrote the lackluster Luna Eclipsed - in case it isn't already clear, I'm not a big fan of Luna).
Yeah, Scootaloo did try to act not scared to impress RD, but at the end of the episode, it was all what the fans call "Scootalove", so... yeah, pandering.
The only S3 eps I'd give an A- or better to were Magic Duel, Apple Family Reunion (I'd put money on the ending scene being classed as one of the most iconic scenes of 2010s cartoons ten years from now), and Magical Mystery Cure (the finale, and even this is subject to change, as McCarthy has tweeted that it's the first part of a three-parter, of which the last two parts are the first two S4 episodes). Still, I think MMC should've been saved for a series finale, not a season finale.
Having said that, Keep Calm and Flutter On (the Discord episode which you alluded to) did provide us with an epic reaction image for when someone lands a sick burn.
Still, I feel that MLP has already contracted "Spongebob syndrome", and this "disease" will, unfortunately, probably be terminal, in my opinion.
Anyway, my main point is this: Corey Powell is not a good writer, because her writing is just so lazy. To me, in any work of media with a script, lazy writing is the cardinal sin. For example, in a rare case which bucks the shark-jumping trend, that's why I prefer S3 and S4 of Adventure Time to its first two seasons: S3-4 had more daring, ballsy writing, while S1-2 had lots of lazy writing (and, indeed, in the beginning, I hated Adventure Time; I like it now).
Regarding Simpsons DVDs, I recommend the following episodes:
(All episodes are seasons 1-5 unless stated, as I feel that it started its ascent over the shark during the back end of S5, and finally jumped it somewhere in S7.)
Flaming Moe's
Homer at the Bat
Lisa the Vegetarian (seventh season, but this was actually good)
Lisa vs. Malibu Stacy
Marge vs. the Monorail
Last Exit to Springfield (generally considered to be the magnum opus of the entire series)
Marge in Chains
Bart Gets an F
D'oh-in in the Wind (tenth season - by now, the show had jumped the shark ages ago, but this was a rare gem)
Homer vs. Lisa and the 8th Commandment
Bart the Genius
Dead Putting Society
Deep Space Homer
K-on DVD? Pretty cool. Actually, sometimes K-on airs on TV over here - we have an all-anime channel, called Animax.