If I had to wager a guess, the queue system itself is working fine. What we're experiencing is in part being the victim of our own success.
Just like dungeons and the LFD tool, Battlegrounds are hosted/located independently on its own server. As such, I stipulate the following:
1) Blizzard has limited space for active battlegrounds. 4-5 years ago, when BG's were first implemented, you could get instant queues at 60, or at least I remember for a time I could. However, with time, as the game populous has grown, I suspect the servers have as well, but not at the same rate. As are result, you have a wait time to get in an active BG slot, not so much because there is a faction imbalance, but because there are not enough active slots on the BG servers--in general.
2) Given (1), Blizzard has prioritized space/active BGs and allocates them to their larger demographics first. This would seem to fit--85 queues are a bit shorter, but there are also many more 85s than 70s at any given time in queue. Blizzard also prefers their players play at the highest level of content, so this comes naturally, given the 1 point.
3) The 70 twink population is actually growing, not rescinding. Considering how many XP-off AV queues hit (i've experienced a few myself), there are more people queuing at any given time. If (1) and (2) are true, then this would follow. Why would the queues be longer? More people waiting their turn. It'd be one thing if there weren't 80+ people for AV, but the fact of the matter is AV's popping. I think we've just hit our BG threshold.