Aim doesn't matter in insta as much as it does in NW.
IG is all hitscan. However the gun fires fast as hell and actually is a kill on a larger area. In NW the closest guns are the LTG and shock. The LTG forces you to aim on the head for the instant kill, and with the shock if you can keep the cursor dead on them you can repeatedly bounce them for an near instant kill (those 3 shots go fast). That takes a lot more aim then the insta shock.
That's why NW players tend to have far better aim then IG players. My aim becomes worse the more IG I play. Yet when I walk into IG from NW I can hit insane percentages.
I'll admit aim doesn't translate into kills. You can take a ton of shots and miss a lot of them yet get a lot of kills. Or you can take a few shots and get a small amount of kills.
The thing about IG is since it's void of all strategic elements (no items to control, no guns to lock) the "take a lot of shots who cares how on point they are" logic takes hold. In NW it's not about the kills, it's about the control, so all the shots you take had better be dead on, and count. There is also the issue of having to deal with prediction shots, and mid air projectiles that aren't instant hit. It's easy to nail somebody out of the air with the LTG or shock (in fact the engine makes it easier then it is to hit them on the ground) pulling a mid air rocket or flak bar is a far more compicated matter.
ICTF is fun because it bucks the more advanced stratey and skill sets and let's you get down to the meat and bones of CTF... the flags. It's very addcitive and far more fun since you don't have to worry about the status of 20 guns 2+ armors, a keg, and the DD. IBR is fun because when in IG LG you can pull some sick mid air interceptions, and like ICTF you don't have to worry about the more complicated issues.
I agree with you on maplock, it's not fun. In fact it's brutal. But that's just part of the game and map lock tends to seperate the noobs from the decent players. Top level map lock is outright vicious. I've handed people 1v1's where I forced them into the negatives due to map lock... I've also been worked that bad as well.
Rainbow Six is a great game, and I agree with you on CS. I can't stand it.