Maybe they were armed with melee weapons only or had weak pistols - how do we know he killed them with bare hands?
CJ is more ruthless because Niko only kills for money, but CJ sets up work and does anything to get the thing he wants. (example Sweet released from prison.)
Being ruthless is doing something without pity. Basically killing someone with no reason would be ruthless. CJ obviously had a reason and I think his reason is a lot less ruthless than Niko's reason.
I'm pretty sure they mentioned that Tommy did it with his bare hands in the game. Why don't you play it again.