Sorry perhaps I was too snarky. I’ve heard too much “dElVer isNT a pRoBlem, iTS jUsT MtGo mEtA” over the years.

I am using the statistical definition of significant: not due to chance. The actual observed difference is in the numbers on the left.

People want to feel like they can beat the best deck if they play tighter than the opponent. The stats bear out that it isn’t true (-EV is about the same as the + EV of being a good player). But there is also the intangibles you mention. Magic is so full of haymakers nowadays and games end immediately. When the delver opponent plays an unkillable 8/8 on t3 and always has the game ending hate card because of EI + DRC you can’t kid yourself that maybe you could have played it better. You lost because they are playing the WOTC $$$$ Mythic and you aren’t.

They forced your answer to murktide? Nothing you could have done. You’re dead.
They always find their 2-of meltdown by t3 against your shortcake deck? Nothing you could have done. You’re dead.
That’s the sort of intangibles that makes people quit or play delver.