Lets put it this way: Healers matter, A LOT - But I've had a 10 dps team MOP THE FLOOR with a 3 healer 7 dps group many, many times.
It's about the people you are playing with, the skill level, how many bots are on the opposite team etc.
Don't overthink this, Rando BG's are rough sometimes.
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BTW, this is a ratio on my main toons for win ratio per faction. This is US/NA division:
Dacoolist - Darkspear (Alliance): 743 of 1,161 bg's won [64.0% win]
Dacoolist - Mal'Ganis (Horde): 432 of 674 bg's won [64.1% win]
Dacoolest - Darkspear (Alliance): 303 of 482 bg's won [62.9% win]