So either Sanguine + Volcanic is a very easy combo (it does seem to be quite easy...) or my group is just getting better. Likely a combination, which is why I like the Mythic+ system, if you do it with the same people you really do start to notice your synergies getting better. Normally we are able to do +5-6 pretty easily with 2 chest, then have a bit more issue with the +7, and we've been 1 chesting 7-9ish. But this week, we got +7 Black Rook and we were only ~2 minutes from getting a 3 chest, with no deaths the entire run. Felt really good. Now if only our group could see some of these increased legendary drops people are talking about, instead of just me as the tank having the almost worthless Cinidaria and our healer having Sephuz...
Also the fact that the travel form epic mount speed change works in instances and works with the version other people can ride is the best change of 7.1!
sanguine/volcanic is probably the easiest unless sanguine/overflowing is possible (that would be a total joke).
However I've noticed some things with volcanic. It's either being spawned by boss adds or is affected by boss attack speed. Melandrius (final boss of Court of Stars) was spawning them so fast that nobody in our party could stand still for even a second. Towards the end of the fight they were being spammed so fast that multiples were coming up under my feet at the same time even as the tank. Very strange and annoying.