No it's not. Melee was already a very strong game and was largely being rallied to deal with an even bigger rally. It rallying its way past Chrono Trigger is annoying for some people, sure, I get it, but it's hardly some ridiculous thing for SSBM to beat CT here. And, ultimately, SSBM's rally failed.
It has been very clear for like 7 years - for some, as many as 13 - what kind of rally this site and this community will accept and what kind it won't. Those lines in the sand are very clearly drawn by now.
1) don't be a really shitty weak entry that suddenly gets propelled to god-tier. This is made especially worse if you then completely abandon it later. 2) don't have a trollish fanbase on this board/don't help turn the board into a toxic soup 3) don't be too esoteric and exclude the majority of people, especially the majority of people who play close attention to the contests.
L-Block admittedly does #1 but is absolutely not guilty of 2 and 3 since almost everyone was in on the joke. SSBM doesn't fulfill any of them. Undertale very obviously does 1 and 3, and during the contest there's an argument for 2 as well. But it was still better than Draven, which ticks all three boxes a dozen times over.
Admittedly the list isn't exhaustive and there are slight exceptions; Draven had other stuff on top of those such as the downtime during Link/Draven/Shephard fuelling the hate for his rally, but that's a unique situation so I couldn't list it. And Mario is in no way esoteric but some people turned on him in 2018 after he rallied his way past Samus. But he still only lost to Cloud by a hundred or so, so who knows how much that was actually a factor.
Probably you could add "don't actually win the contest" to that too. If Undertale lost to SSBM its rally would be more accepted, and SSBM's would be less accepted. Starcraft's in 2004 is mostly remembered fondly, even though it actually cheated, and part (not all) of that I'd say is because it didn't actually win or even threaten to win.
Acting like all rallies are equal when they all have very different effects on people is silly. And yes, sheer game preference is a factor, I won't pretend it isn't.
I don't see how I can lay it out any more clearly than I did here. If the actually sane "there's no middle ground" people want to actually refute this stuff then great, otherwise it's just thoughtless.