I'm not a fan of de-crowing either. Although personally, I find that an operation done by a professional under anesthesia is preferable to caponizing - something I personally do not accept at all, at least not the way I've seen the procedure described. "Holding some ice against the area" is not an acceptable form of pain relief.
I'm not a fan of the way pigs are sterilized either, but I can understand why it's done. But doing it with pain relieving medication (something that at least here is becoming more common) is a great improvement to the traditional way of ripping them off and leaving the animal with it's pain.
Castrating is something I grew up with - be it by knife or ring - on sheep and cattle. Normally we would do 50-100 steer calves or 200+ wether lambs in a day. Observing them, the knife style return to normal behavior more rapidly. Fast forward 30 years, and as many years of surgical and pain management experience and I had to castrate pigs. The procedure takes a novice like me about 15 seconds a side, and the piglet returns to normal activity in under a minute.
Do they feel pain? no doubt. Does it hurt more than being pushed through a birth canal? not sure.
If it was delayed castration I would use local anesthesia and analgesic