As an engineer you must be good with numbers. Age 66 is considered “young” these days and if you are in otherwise good health, even younger.
As others have suggested, you really need to pin down those biopsy pathology results, because if they come back with cribriform (intraductal being more aggressive), coupled with your very high Decipher score, you have a type of cancer that statistically has a greater chance of recurring after treatment (any treatment).
That doesn’t mean it WILL, but it could.
With that in mind, perhaps surgery might be the better option. Once the gland is removed, the pathologist will view it as a whole, EPE will be absolutely known as well as any breaks in the capsule, lymph node involvement, etc.
Hopefully, all will be negative. But if not you will then know if you should go on ADT and receive radiation or perhaps monitor your PSA’s on a 3 month basis. Any recurrence down the road (even many years later) can be treated with radiation.
I know Proton therapy is supposed to be kinder to surrounding tissues due to the Bragg Effect, so not sure if salvage surgery is more successful in these cases or not.
One other thing I would add: get a second surgical opinion. Your current surgeon sounds very honest and forthcoming (a lot are not) but the way you present it, it almost seems like he doesn’t want to do the surgery for whatever reason. Not sure if it’s a lack of experience in a complicated case, but you want to find the VERY BEST if they are gonna be cutting down there! Best,
Phil

My urologist at Sibley Hopkins gave me the biopsy report of intermediate unfavorable and subsequent Decipher was 78 high risk. I'm older at 78 but he was strongly recommending radiation over surgery. So I did Proton Therapy at Hopkins which I completed a month ago. I also met several men there with prior RP who were there for salvage radiation. Happy with my decision but underscore that it's yours alone to make in consultation with your treatment team rather than any recommendations you might get in this thread or others about which is the better option. Good luck!