You might be overthinking this? When you thought/knew you had (at least) 3+4=7, you were still in the "intermediate favorable" category and you could consider radiation or other forms of ablation (using other ways to "zap" certain areas). But, like me, you got news that things are (likely) worse. In my case that was a second node of concern on a repeat MRI and two 4+3=7 on biopsy.
At that point, I no longer qualified for the (new form of) ablation clinical trial and I was advised that RP was a preferable next step for all the reasons that have been discussed. (The research urologist said he had treated a lot of post-brachy recurrence in his own practice and he felt I was not a good candidate for that with my diagnostic indicators.) This was confirmed when the RP revealed positive margins and some more advanced cancer cells in the prostate. I felt bad about losing options before the RP, but mostly bad knowing my cancer was more advanced than I had hoped.
Now I'm in the waiting for BCR stage not quite two years after RP. In this case, I'm glad I'm still waiting, but disappointed the latest uPSA was higher than previous ones. I prefer sober reflection to flights of optimism, but I can guarantee that others experiences will differ in that regard :-).