Do rats, mice, birds, bugs or anything else you take the life of suffer when you try to kill them? Have you never wounded something and it get away only to be found later dead because of your actions? There is no difference. You're just trying to make the debate about the pig because it is a bigger vermin than say a rat or bird, ergo it should suffer or feel more pain than another animal.
I don't really concern myself with the antics and actions of PETA and other anti-hunting groups. You have crackpots and tree huggers everywhere and you always will have them.
How about fish? They suffer, being drug up from the depths until their eyes pop out, with a hook stuck in their mouths and then thrown into a cooler of ice. They flop around on the deck and bleed or get clubbed. Do you think they are suffering? Do you think they are feeling pain? Is it any different for a 1lb bass than a 600lb tuna? They are both fish as a rat is vermin just like a pig.
Your logic holds zero basis. Killing is suffering be it a bullet in the brain, lungs or guts, getting yanked out of the water, poisoned, being stabbed or skewered by an arrow. It's never pretty and quite honestly never really ethical in the sense of pain and suffering. How do you feel about a bowhunter who shoots a deer and then they "back out for the night" to let that animal bleed out because "they may have hit it too far back"? Is that ethical or acceptable since it is bowhunting?
I don't lose sleep over a fish I threw on ice, a rat I poisoned, a fly or bug I crushed, a deer I shot too far back, a bird I winged or a hog I shot in the guts. I don't lose sleep over anti-hunting groups or people who don't understand eradication of nuisance animals. I do make the best of the situation presented in recovery of a game animal I shot but, I'm not going out of my way for a pig/rat/mouse/varmint. In fairness, the natural world is far more cruel than a man with a gun will ever be.
https://www.youtube.com/watch?v=WtVXFonpaWo