Look at all these variables here. First of all, we need to get one of the small BGs, then we need to roll bad team mates while the enemy doesn't, then we need a particular player with the gear, spec and willingness to switch as opposed to doing what most people do and just continue playing the spec they want to play because this is a random BG that they joined for that specific reason, then we need to gamble some more that this particular player switching will make any difference whatsoever. And at the very end, we need to realize that all of your issues are easily solved with premades. Something I find funny is that if your concern is balance, why do you think someone switching to DPS or healer is gonna make a bigger impact on it compared to both teams having equal average gear level? Because it wont.