cav·i·ty/ˈkavitē/ - An empty space within a solid object
If there's a space it's not a muscle back or blade. There no reason to change the definition of blade when the one for cavity back is accurate.
OK, how about the Ping s59? It has a big muscle bulge right underneath the shallowest of cavities. Actually the whole Ping s line has some variation of this. And someone pointed out the Calloway x forged. Or how about the W/S FG tour V2. There is actually an abundance of these shallow blade-like CBs. How about putters being called blade putters? There are no real blade MB putters except maybe for the one Lefty used to use 10 years ago.
I was just suggesting that maybe the definition for the term 'blade' could use some loosening up, but I guess too many here are stuck and fearful of change..
I think over time the generally accepted definition will loosen up to include players cavities. Probably has already started to loosen up.
Of course it has loosened up. There are guys shooting high 70s on 70 rated courses calling themselves scratch and guys playing off 9.9 calling themselves single digit so why not?!? Whatever brings more posers players to the game, eh?