this goes in detail, but claws are thicker, and physically closer and more wrapped around the bones, and they not that fragile

That doesn't make them "closer to bone" than they are to nails. Handling a cat makes it very clear they are much closer to nails than to bone.

this will impact their preying abilites i think

You think wrong. At worst their claws are a little dull for a day. Cats sharpen them by scratching, and because claws aren't bones and closer to nails it happens quickly.

indoor cats do spend some time outside

Then they're not indoor cats.

Also, your cats are rescue cats, so they also have some amount of trauma, and may explain some amount of fear.

One of them has a scratch, the other was rescued too young for any trauma. Certainly nothing related to their nails. They don't have a trauma response or a fear response, they just dislike it (same as human children often do). Stop assuming.

It is not just a way to do what they naturally do, naturally they get experienced in hunting, and during that, they wither their claws. It is a more gradual (not a discrete clip 1 mm in a day, a month together, as compared to a few microns every time they attack).

That's not how it works. Your lack of experience handling cats is really showing here. The claws wither because the cats walk around on harder materials, like stone, wood or the pavement. This 'chips' off parts of the nail. They don't need to hunt for this, it just happens as they walk around. They're also not losing microns this way, they chip off bits or 'slices' off the nail, usually a couple mm long but quite thin. A house cat will also do so, but at a slower pace because house floors are less course and rough.

Also, the experience (and the reward of food) is now replaced by trauma, and some treats.

Cutting nails is not "traumatic" to a cat. Stop presenting this as a fact when it is clearly not. Most indoor cats don't even mind at all. But cats are drama queens. 10 minutes late giving them food or cleaning the litter box? Time to yell throughout the house as if death was imminent. Anything they dislike and they're more than happy to thoroughly inform you of it. Oh a treat? Nevermind then it's all good.