Also a good chunk of "good" Mastery is now Glammour there's a difference between the two pillars then and the two pillars now.
Altough I am sure they were some tensions between the two pillars when Mastery was legal, for exemple in diplomacy now uterly dominated by Glamour practicer not so much before.
There's also the fact that Glammour is the most widespread pillar and supposedly the most "easy" to learn. I would not be suprised that in some Mastery circle, Glammour is the lesser Art, a gateway to the real Art that is Mastery. (a bit like calligraphy/Orthography).
Altough now I wonder if Glammour/Mastery mastery was in anyway common for mage talented enough to master more than 2 pillars. The two seems to synergise nicely.