Kalos is notorious for 'feats' like that, and most websites that routinely talk about power levels like WWW and ComicVine would throw them out. Those battles were aborted, and even before they were aborted they were too vague and contradict later events. Nobody's going to accept interpretation-based evidence when there are much clearer feats in later Mega Evolution Specials and anime episodes.
Here, SM129 gave us solid, unambiguous feats of defeating multiple evolved Pokemon, often in a single hit, without any time for recovery. That is damn impressive, and Pikachu's performance here might be his best to date, save the defeat of Regice and Latios.
SM129's feats are as ambiguous as SME act 3, the pokemon ash and kiawe beat (aside from magmar/electrivire) have absolutely no previous feats whatsoever, so we don't really know how strong they really were. Meanwhile, we saw Kyogre being able to take on M.Metagross' meteor mash without much issues (something tangible), and Groudon was around the same level of power as Kyogre, we then saw Charizard take a surprise Precipice Blades to the gut and not only survive, but not get de-mega'd (like usually happens when a mega gets defeated), though it still took a lot of damage. IDK what there is vague. Then, Malva's M.Houndoom was able to take on that same M.Charizard at full health (although low on stamina) and give it a good fight, I doubt such a pokemon would fall to Turtonator.
You have no way of showing that an E4 is "a lot more" powerful than Turtonator, a Pokemon that
-almost knocked out Mega Steelix, evidenced by Steelix's steam breath and Brock's comments
-defeated an Alolan Sandslash, Magmortar, Electivire, and Metagross with little effort in the same battle with no rest
-tanked a Salamence Flamethrower and hit it hard with Dragon Tail
Note that the Mega Steelix battle happened almost 70 episodes ago, before Turtonator learned Shell Smash and spent all that time training for the Pokemon League. Given what we just saw, it would probably win this time.
By your own admission, Mega Pokemon are powerful. So to say Turtonator isn't E4 level, you have to show
-all Elite Four are equally powerful (not true)
-all Elite Four Pokemon are equally powerful
-all Elite Four are above Mega Pokemon
I didn't even argue that Kiawe was E4 tier, I personally don't think he is, but there's no way to prove it either way. Elite Four is a title given to trainers who are said to be strong. Unless they demonstrate, we have no idea how strong they really are.
We just saw an episode where a Pokemon proved he was strong by beating Pokemon that are consistently portrayed as strong, in unfavourable conditions. Turtonator was ganged up on by Electivire (who previously defeated him) and Magmortar, and he obliterated both at once.
To me, saying E4 are still above seems is putting the title before the feats. I'm going to trust what I see over what I'm told every single time.
-Steelix flat out just stood there (though on guard) against the Z-move, without trying to counter it or do anything else about it, he did a lot of damage, but that was partially because of type advantage, a good feat, but an issue is that steelix has nothing to really compare to (his only other feat was beating other featless mons from TR HQ commanded by jessie and james), and megas can vary in strength heavily, even between gym leaders, as we've seen with Korrina's M.Lucario and Wulfric's M.Abomasnow
-E4 mons and members aren't equally powerful, you're right there, but even then, I really doubt Turtonator would beat a lower tier E4 mon, highly damage, yes, but beat, I doubt it, as E4 members have been portrayed as almost unstoppable forces before XY (and even then the only one capable of beating an E4 mon well was using a horribly OP pokemon)
-Like I said, Megas vary in power, so that statement is already flawed because there's no single "mega" level
-You said that a +2 IO from Turtonator would beat M.Houndoom, which implies that you're putting him in the same level as an E4's mon
-Ok then, go by what you saw, if you've seen E4 members fight, you've seen that some of their pokemon are able to:
Destroy pikachu and infernape with negligible effort, wreck torterra, tango with cynthia's garchomp, and that's not even getting into E4 megas