And you saying "Glad was never particularly hard" makes me believe you're one of those people who diss TBC just to diss it. If you were any good during that period, you'd see that there was actual competition back then.
This... There has always been the broken stuff
s1: stormherald, pally/war in general
s2: druids started showing up, sl/sl
s3: Warrior/Druid beat everything, glaives started becoming a popular thing, sl/sl
s4: Ret pallys, glaive rogue/druid
s5: Dks, ret pallies, holy pallys, bm hunters, survival hunters..... list goes on
s6: Frost death knights, destro warlocks, ele shamans, beastcleave, ret pallys... list goes on
s7: prot pally healers then later ridic prot pally dps, prot warriors, armor pen warriors, still destro locks
s8: wizard cleaves of any variant
s9: ferals, mages, warriors, frost dks, enhancement for a while.. list goes on
s10: no one played enough for anything broken to exist because it was so fucked, but legendary staff..
s11: Legendaries/cunning/vial/heroic DW weapons, 5x tentacle proc soloing you, RLS, triple dps, LSD2
s12: 5.1 warriors/hunters/spriests/mages etc
s13: first half - spriests/hunters/mages/rogues broken, second half - we'll see...
I think glad started losing what little merit it had when cata came out, IIRC s8 was still pretty damn active (50~ slots for glad). My friends and I were talking about this the other day. Something that made Wotlk, and BC to some extent fun was that you could be successful playing just about anything if you played well. For example, in s8 we played enh/war/rduid to 2650ish when our BG was overrun with MLS and Double Healer with some LSD sprinkled around. We would almost always lose to the mage teams due to no dispel/freedom for nova, but we beat double healer so bad it kind of balanced out. You can't do things like that anymore though, how often do you really see a "unique" comp at a high rating these days?
Every single team above 2200 on my bg has at least one, if not two of the following: Hunter, Mage, or Spriest.
I would say glad is probably a little harder if you play a team without one of those three classes this season.