This is exactly the issue, but your calculations need a couple of corrections. The largest of which is that when you do 50% discharges, you need to do twice as many cycles. That would mean 6 cycles per day in your example at 1.2 kW-hr per day vampire loss. On top of that, this kind of draw is an 8-hour draw for 100%. Looking at the chart at the bottom of
https://www.cdtechno.com/pdf/lit/12_1061_0412.pdf, it gives a capacity of 30 A-hr rather than 33 A-hr at a 24 hour draw. That increases the cycles per day to 6*33/30 or 6.6 cycles per day.
If you assume 1800 cycles per battery that the spec sheet claims, the net result is 1800/6.6 or
272 days battery life. Because the vampire is sometimes less thirsty than 1.2 kW-hr/day, the vampire stops drinking when the car is on, and the batteries probably do better than spec'd, we usually see more than a year from these batteries. If you want your lead-acid battery to last longer, then use all the power savings modes to make the vampire less thirsty.
The reason that these batteries fail so often is simply because the vampire is sucking the life from them. A larger, heavier lead-acid battery could last longer, but the real solution is for Tesla to improve sleep efficiency in the Model S. The Roadster has a MUCH less thirsty vampire. My guess is that it will take a major hardware rev of the processors to tame the vampire. With all of the other development going on at Tesla, I bet this is just low on the priority list.