I dont gut hook fish very often, it would be impossible to come up wth a *average guthook ratio*.. it depends on the habits of the fisherman, and the feeding mood of the fish.
I always get the hook out if there is enough of the shank exposed to manipulate the directon of the hook. Grabbing the hook and carefully rotating the hook in the proper direction for the barb to come out usually works. By the time you get the hook turned 180 degrees, you just pull the hook out backwards and they pop right out.
I dont go through the gills. I usually am not fishing for fish small enough that would require going in through the gills… Flatheads you just reach in and carefully do your removal and hope you can keep the mouth open so they dont chew on your forearm while your removing the hook.
I probably gut-hook more sheepshead than anything in the fall while sturgeon fishing. One or Two sheephead are a welcome addition to my cut bait table so any means neccessary to get my hook out is acceptable
I dont see why on smaller fish a person couldnt access a deep hook from the gills if being very careful.