You have example in this very game that this solves the issue, CT dps queues were awful, ST and WoD replaced just ONE tank to dps and bam, dps queues are way better than tanks(although if we had 10 per party with 2 extra dps it would have made dps queues better without screwing tanks queues nearly as much). The CT change isn't even close to being as drastic to simply changing the party setup standard to 5 man and adding 1 dps. It would work, and they should implement it .
It may not be that simple. DPS queues (at least on my data center) are great for LotA on Tuesday, and absolutely abysmal on Monday. Why? Because people are doing the weekly on Tuesday and not doing it anymore on Monday. Personally, I'm of the opinion that the change to the number of tanks in ST and WoD wasn't so much to help DPS queue timers as it was because they ran out of things for six tanks to occupy themselves with.