I was taking a couple of different approaches to the raid bosses, and so far it looks like my best work has been Cattleya, Herbaceous Pony (Halloween), Cherry, Kerria, and Alpinia.

My numbers went up when I put taunt on both Alpinia and Kerria, putting my average time out is at 11 million. Felt strange to do it on both of them, but having it on Kerria as well let Alipinia survive the whole fight every time and still get a good number of counters in.