Having laser accurate, armor crushing rocks flying at the speed of light is a tad bit unrealistic one might argue.
Also from a gameplay point of view looters are (or should be) the weakest troops you encounter on the map, so a new player with a low level character can both learn the game mechanics and grind some exp. before getting into bigger challenges.
I personally don't mind their accuracy, I don't want them to throw like headless chickens either so I can just waltz in unscathed on my horse. Damage is another story, of course armor should diminish blunt damage, otherwise you feel your armor does nothing, so I do agree with damage adjustment (not by nerfing stone damage though, but by buffing high-tier armor, so that you feel a sense of progress).
Realistically, looters are still humans, so all in all it's immersive for them not to 100% suck like in warband. I like these new looters a lot more. No matter how skilled a warrior you would be, you would still get outnumbered easily and defeated by a bunch of unarmored thugs, so still you shouldn't be a god amongst men just because "they're the lowest of the low", and having some sort of tactics or at least some skill against them should still be a necessity.
I really don't agree with the new player argument. How long is a new player "new"? Even if you make looters be tougher enemies, a player should adapt after a few hours and learn from mistakes. Making the game unreasonably easy and casual isn't a solution, it will just hurt veteran players more. If I play on all realistic settings, I expect a little bit of a challenge in every part of the game. Players that want less of a challenge have different settings they can choose. Also, a new player can easily choose his fights as long as he keeps horses in his party (not even that necessary early on), doesn't carry too much, and knows how to recruit from a village. The game is pretty newb-friendly already I would say, it's a casual sandbox experience, it's not rocket science. This is not prophesy of pendor, which mind you I had no trouble adapting to after getting defeated a couple of times by some troop I didn't expect to be as tough as it was that mopped the floor with my recruits and me. It was very enjoyable to learn and overcome the challenge. That mod was the best experience that warband had to offer for many players including myself, and the challenge was a big part of why that is.
If looters had a leader, which was tougher and had good equipment, I'd be more than happy with that. If looters raided low-militia count villages, I would also be happy with that. Taking into consideration what more challenges could be placed into the game I think they're fine, apart from the damage that is not mitigated by armor like I stated in the beginning. That's the only thing I would change.