That's how it used to be, but it's not any more. A GC army can include any models from the Arnor list, including Warriors of Arnor. If you include a RotN or Dunedain for every 4 RoA, you can take as many RoA as you want and they can all still shoot.

Obviously this means if you take 24 WoA and 12 RoA, there is no point taking any RotN at all. You'd only use the option if you want to go above the 33% limit...in essence you can pick any "limit" you want, as long as you have enough RotN or Dunedain. If you wanted to take 16 WoA and 16 RoA, you'd need to add 4 RotN though, which is 100 points more expensive for minimal gain.

I'm not sure at what point, if any, it becomes worth it. GC used to be overpowered. Now I think they're underpowered, even with a 100% bow limit, because RotN are expensive, but still only have 1 wound.

How is what you're saying any different than what Narsil said?

Narsil said you can't have Warrior of Arnor and Rangers of the North in the same army list whereas whafrog said what I said yesterday, that you can use them both but you have to choose which bow limit you will follow (either 33% or 4 RoA per RotN) i.e. ou can take 2 warbands of Rangers of Arnor, (24 total) with 8 Rangers of the North, and then take a Warband of 12 Warriors of Arnor.

Yes, that's why they aren't particularly competitive any more.

And, I meant 6 Rangers of the North.

They don't seem particularly uncompetitive, I mean Aragorn for any army at five hundred is a bit pricey.