What's best forum...

As long as the 'grunge' is avoided by keeping cone excursion below ±1mm or whatever the limit is for a guitar speaker, it could a near-perfect mid-range, AFAICT.
Limited cone excursion is only a small part of a guitar speaker's 'grunge'. Designers talk about 'cone cry' which makes up most of the midrange sound.

But if you're happy to use a Celestion G12 as a mid, they are happy to sell you some. Now you just have to choose which one 😉
 
Why is it that whenever EQ filters would be the perfect solution to solve the "obvious lack of EQ" problem, it's treated like some advanced alien technology that mustn't be used, in case they come after you?

Until someone shows the data with painfully high distortion from said speakers, I refuse to believe it's somehow baked-in. Otherwise it would be impossible to un-grunge the sound when the playing is clean and without over-drive.