The radiation you are currently receiving is completing the process and will bring your PSA much lower.
But even with ADT, prior to radiation you still have a prostate, and yours contains a more aggressive cancer, so it is STILL producing loads of PSA. Ergo, your single digit number.
So to me, your pre/radiation numbers look really good and nothing in them portends an “a priori” castrate resistance.
What @stew80 posted only makes sense. More aggressive cancers, evidenced by higher Gleason scores - especially those with metastasis - are simply stronger, faster and more resistant to conventional therapy; their tendency to become CR is yet another facet to their innate aggressiveness.
Once CR occurs, it’s a whole different ballgame and the drugs involved in treatment come with side effects as well - some much more serious than “simple” ADT. So it really is in your best interests to pursue “the gold standard” with fingers crossed before you pursue the “mine is different” route.
Phil