This is a very interesting system/method. However, in less I am missing something you are not using your margin efficiently as you could and thus could get even better returns.
The position set up you recommend includes a DITM call and slightly OTM put. However this is synthetically the same as using an OTM Put and a slightly ITM call. The big difference between the two is although the risk is the same, the cost (margin) required for your set up is 5 - 6 times greater than the cost of the synthetic alternative. I confirmed this with TOS as well as modeled it out. So this is a big opportunity to trade this in a much smaller account as well as having much better results if you use the same amount of margin but use the OTM options.
Secondly, when comparing to buy and hold, you do need to consider that the SPY does have approximately a 5% annual dividend which of course you do not get when using the long term options.