Yes, finding discussion on this topic is difficult. Anecdotes aside, even the most authoritative treatments seem mostly...anecdotal :-). So I'll spare you mine :-).
Here are things I think I know at this point:
1) Orgasms happen in the brain, not in the erection.
2) Trauma is a big deterrent to orgasm, and perhaps surgery is more traumatic than radiation, but maybe catheters are more traumatic than surgeries? I guess only the first of these three is something I actually know or think I know.
3) Erections have a lot to do with blood flow, valves, and nerves. PC treatments all affect blood flow and nerves, somewhat unpredictably. Valves deteriorate with age.
4) Surgery is especially traumatic to the nerves, but there is often some recovery over time, maybe up to two years or even longer.
5) Radiation is progressive, so initial experience after radiation does not tell the whole story of the ultimate level of damage.
6) The brain can be retrained. (See 1.)
7) Erections can be preserved or strenthened via increased blood flow, either muscle tensioning or vacuum erection (mechanical) or sildenafil/taladafil/etc. (changes nitrous oxide levels, I think) or trimix etc. (chemically triggered erections.
8) Surgeons ultimately promote penile implants even if they are ostensibly educating about other strategies. Boston Scientific sponsors education because they are the biggest supplier of penile implants in the US.
9) Yes, it's true. Post prostatectomy erections are always dry because the tubes carrying seminal fluid have been severed.
[Feel free to disagree with any or all of these things I think I know, and I'd love to hear why.]