It's not really a big example when he didn't even lose the game to it. The fact he immediately even stocks out and proceeded to still lose, to his own bad DI no less, is not an example of rage determining a set.
I looked up his track record at tournaments, and his only loss to a Corrin in pools was Blue Beast, who who beat 2-0 in the pool finals. The VOD of his loss doesn't exist, so there's no real way to extrapolate on how he lost the set. It could've been player error, it could've been gimps, but we don't really know. As with the Prince Ramen example where ZeRo simply made mistakes and got outplayed, it's presumptuous to assume that that was due to game mechanics.
Ally's losses in 2016 out of 28 tournaments:
Dismantle 2: DKWill (1-2), Nairo (1-3)
Southern Ohio Smash: Zinoto (Game #s unknown)
Wombo Wednesday 21: Shaky (1-2), Ranai (0-2)
GENESIS 3: Ranai (1-3), Nairo (1-3)
Frosty Faustings 3: JJROCKETS (1-3)
Landlocked: Ryuga (1-3), Dabuz (0-3)
Breakout 2: Zinoto x2 (Games #s unknown)
Shots Fired 2: 9B (1-2), ANTi (1-3)
OUTFOXX'd: Mr. R (1-3), Mr. R (0-3)
Pound 2016: VoiD (0-3), Abadango (0-3)
ConComics 2016: Hyuga (0-3)
EGLX: Mew2King (2-3), Nairo (0-3)
NEW FISH: Larry Lurr (1-3), Larry Lurr (1-3)
Momocon 2016: Wrath (0-2), Nairo (2-3)
Smash n' Splash 2: Ned (1-3)
Breakout II: AoH Vanity (0-2)
CEO 2016 Blue Beast (0-2), Zenyou (1-2)
Midwest Mayhem 4: 6WX (2-3), Hyuga (1-3)
Clutch City Clash: Samsora (0-2), Samsora (2-3)
Super Smash Con 2016: 6WX (1-2), VoiD (1-3)
Endgame: Mew2King (1-3), ZeRo (1-3)
Out of the 34 set losses in 2016, only 3 seem to be particularly unusual. You could call his losses to JJ and Shaky abnormal, but in fairness, both have some impressive accomplishments and could feasibly drop a top player, especially as early in the year as those losses were taken before Ally had even broken out with huge wins. Same applies to DKWill, especially since the common viewpoint at the time was that DK > Mario in terms of matchups.
Ned, Wrath, and Samsora all appear to be totally worthy players with good accomplishments. Wrath has not lost a set to anybody in GA in months, Ned has beaten Zinoto and continues to be a challenge for Ally, and Samsora had a grand total of 7 games, the last of which one where Ally made a critical SD that robbed his already waning chances of a comeback.
I can't comment much of his loss to Vanity, besides that:
-Ally stated he was really good
-Vanity made 9th at the tourney, getting beaten by Blacktwins, who went on a roll and even bested Zinoto, getting 4th at the tourney.
Games 2 and 3 (the ones Zenyou won) of Ally v. Zenyou are online, and judging from the footage, both simply played evenly. Zenyou has accomplishments under his belt, he's 5th on the PR of what's probably the strongest individual region in the world, I don't think it's that absurd especially considering Ally got KO'd by intelligent edgeguarding on Zenyou's part. The game also descended into upsmash wars, but this was after numerous equal exchanges in the neutral.
You could argue that only 2 would be unpredictable, and we regrettably lack footage of either set to make any sort of reasonable judgment call. I would say that, judging by this,
major upsets are rare if he set losses are generally to people at or around his level.
VoiD injured his hand at Mexico Saga. IIRC, it got stepped on when he was trying to get candy from a pinata they had bust open. I don't imagine this is a huge coincidence, considering it's his worst placement of the year and the only other time he scored out of a top 8 at a tourney he's attended.
Because he made a bunch of bad decisions that led to him getting gimped twice. This is what I'm talking about when I say people don't examine the upsets. He played bad and got punished in harshest manner because Cloud's recovery is atrocious if you allow it to get exploited like that. I mean, he literally missed a "style points" Dair to try and finish the guy's stock and SD'd.
ANTi, playing Cloud, got KO'd in the starting seconds of game 1 against Xaltis and overall did not play the set to his best capacity judging by his errors; No footage of Dath vs. ANTi exist to my knowledge, but Dath made top 32 at both CEO and EVO and is generally one of Florida's better players.
While I've already noted his lost to Day was likely junky (he apparently got upsmash at 30-40% and died lol), he definitely is responsible for his own loss against Mr. E, it seems - he airdodges quite a ways below the ledge and can't recovery with Diddy, causing him to lose game 3.
I'm not really at liberty to comment much on the Mewtwo ditto since I have no idea and I'll post it for someone else to analyze, though Rich won Game 1 by punishing either a mispaced Nair or an empty hop on Abadango's part. There didn't seem to be any 2 stock/rage mechanic nonsense happening in the match.
When there are a couple of dozen players, the loser's bracket in top 12/8 is pretty much always going to be stacked, lol. Some people in Loser's weren't even major upsets, given the context:
-6WX had taken a set off of Ally before. Upset, but not a huge one.
-Taiheita beating Marss is definitely an example of Taiheita simply being underrated. Not really much on an upset.
-Mr. R > Zinoto isn't an upset.
-6WX > Tweek isn't an upset.
-VoiD > Pink Fresh isn't an upset.
Part of the reason loser's looked especially stacked is because the qualifer for top 24 naturally throws one of two world-class players into loser's bracket. ScAtt beating Dabuz, while an upset, is not something indicative of massive inconsistency, since ScAtt is a capable player playing an increasingly optimized character.
There were still an unusually high number of significant upsets, but it's pretty bad to accuse me of exaggerating when several of the examples you listed are barely even valid examples in the context of the discussion. E.g., the top players were not playing their best and lost to somebody who was playing the game better at that point. Few of these were determined by "jank".
It's entirely fair. We're talking about better vs. lesser players, but the lesser players happened to play a better game than the "better" player, because the better player wasn't playing to their top capacity or some X other circumstance, lost the set, and got sent to loser's. Nairo's comparison to Dark Souls in a recent interview is pretty apt. You can't play less than your best.
Bringing up Melee again, with not even 2 year sunk into the game vs. over a decade with the other, you can expect less consistency at the top level since the top players of the younger game have lacked the sheer amount of time and history to refine their gameplay.
Basically; The "Smash 4 is inconsistent" comment is exaggerated and the simplified reasons for it are generally not the cause of upsets, and few upsets that happen are true examples of a "random" beating a top player, with numerous caveats and nuances that people often miss.
the top 8s are generally familiar because top players in loser's bracket often lost to other top players in loser's quarters, due to the aforementioned giant pool of good players that make these circumstances inevitable