I've played since the wipe and neither of the realms had "pvp vendors" that gave advantage to anyone. There were promotional 3-5 insta 90 level ups and 3-5 heirloom - contender gear sets.
So this statement is complete bull****.
Merge of Sargeras into frostwolf didn't introduce any balance issues in my opinion.
Before the merge every battle ground I attended with a premade resulted in a 90% win ratio, and the losses were mostly because of rest of our team being filled with under 470ilvl randoms and the enemy had a double premade or a strong premade and decently geared randoms.
Solo ques were always a 50/50 depending on how lucky I got with the team composition.
Number of played BG's: 245
Number of Won BG's: 201
Recent log of REFlex addon that tracks pvp statistics.
So stop crying and get better. - Run premades, double premades if needed.