I've been seeing this point a lot lately and it just doesn't make sense to me. Follow my logic here and please correct me if I'm wrong somewhere.
Non-genesis scenario - Players A, B, and C have rejuv running on them. In a 17 second window (Time offset to accomodate the GCD and application of the second and 3rd rejuv) they would receive 180,000 healing (using my healing partners average rejuv tick of 15k). Healing done during the 17 second window = 180,000
Genesis Scenario - Players A, B, and C have rejuv cast on them followed by genesis. They receive the same 180,000 healing in about 5 seconds. The druid reapplies rejuv to player A, B, and C. Which ticks the full duration on player A, gets 3 ticks out on player B, and two ticks on player C for a total of 135,000 healing. Healing done during the 17 second window = 315,000
What am I missing here that makes this not be an hps gain?
Note: I did not include additional hot ticks from haste for simplicity. But additional ticks would only make the number difference greater.
In the non-genesis scenerio you cast 3 rejuvs.
In the Genesis scenerio you cast 6 rejuvs.
I think that would be pretty obvious. The restriction you have is an artificial one that is saying only 3 specific players can be healed with one spell, making it so any more rejuvs would only clip the previous. Expand that to 6 players on the non-genesis scenario versus the genesis one with 3 players, and you have a better comparison that uses the same resources, with the exception of mana spent on genesis.
Anyway, it is easy to craft a scenario where Genesis increases HPS by setting a specific time interval and player cap. The longer you make the period and the more players you add, the HPS will actually drop in the absence of very specific burst healing. Bust healing is where it will really matter, where your rejuvs would otherwise be sniped.
Anyway, in sustained raid-wide damage, it is actually an HPS loss due to wasted GCDs and mana, I think that is the larger point.