Hm. That's not one fantatsic thing excusing another. ("Wheels aren't square" is just a mundane fact.) No, an analogy to the fantastic-things-excuse-other-fantastic-things argument-you-don't-get would be saying "Build your dog's house out of pancakes..." to the Witch in Hansel & Gretel, who already lives in a house made of candy.
Well... I think his point is that the stuff that bugs him and others like him (e.g. studded leather, mislabeled swords) is not really in the category of fantastic things.
If someone says "How can illithids exist, they don't make sense" I think it's a reasonable reply to say "You're okay with Flumphs but not Illithids? Really?"
But if someone says "studded leather didn't exist, it's a weird nonsensical fantasy armor," I actually think dismissing this with "yeah but you're okay with fire breathing dragons?" is a categorization error.
At the end of the day, all of our fiction has to enable us to suspend disbelief. Everyone has some threshold of believability/credulity that works for them. Those thresholds are gonna be different... wildly different in some cases. But overall, I'd say that torches, studded leather, etc. are all items that are generally considered to be part of the "mundane" world of D&D, not the fantastical one. So if someone feels a particular element of "mundane" D&D is nonsensical and breaks their suspension of disbelief, I think that's a legitimate concern.
I think what he's trying to say is: The existence of the fantastical doesn't mean we remove the onus on the mundane to be within the bounds of credulity. Does that make sense?
It's why people change falling damage, or change non-magical healing, or hate fighter healing, etc. These all stem from the same basic issue, which is the individual threshold of suspension of disbelief, and how credible the mundane aspects of the D&D world are to each person.