Yeah send me the link. I'd love to read it. I can believe it because I see it when I track amps. If you look at the EQ on a spectrum analyzer, you can see a little dip in the mids from any amp. Speakers play a role, but it's there. Hell you can see it on any generic speaker graph.
I think, just my personal observation, Marshalls and other "british" amps may cut and have better perceived midrange because of how they distort. "American" style amps like Fenders and Mesas have huge exaggerated bottom and high ends and the mids kind of get left alone. And they often utilize power tubes that enhance big bottom ends and glassy highs. I think that may be why the Vintage 30 is the preferred speaker for heavy Mesa sounds. The V30 helps the mids. A
Marshall is the opposite. Orange and Vox too. A typical EL34-tubed Marshall has a pretty tight bottom and clean-ish top end. Most of it's grunt comes from the mids/upper mids. Orange amps are thick in lower mids. Scoop the mids on a Marshall or Orange and you still have a ton of midrange sound to play with. I'm not a mid-scooper by any means, but I rarely find myself needing to run my mids past 5 or 6 for anything. It's just too much of a good thing.
I'm looking at the two amps I used last weekend, still set at their gig EQ....
JCM 800 - Bass 7 - Mid 5 - Treb 4
JMP 2204 - Bass 5 - Mid 4 - Treb 6
So average mids, no one that I talked to had any trouble hearing me.