Arlough
Explorer
It's not the only redeeming quality, just another thumb on the scale.
Incidentally, an archer ranger is getting very little from being a two weapon ranger: I mean sure, he gains toughness, but I'd call that even between toughness and defensive mobility given what his playstyle is likely to be, and he's almost never going to use the bigger off-hand weapon, so it's value is very limited.
As for beastmaster: you're giving up prime shot to
*gain a flanking buddy for the melee members of the party
*gain the occasional OA at the expense of your immediate action
*gain a low defense, low hitpoint (once surges are taken into account) resource sponge
To me, that doesn't seem like an automatic choice by a long shot. In fact, unless you're going to choose and use beastmaster-type powers, it looks like a slightly bad deal.
Prime shot, as I see it, requires the ranged guy to be the closer to the enemy than any of the melee-ers. Also, that makes toughness carry a bit more weight, given that the archer trying to attain prime shot is now going to be the "that guy hurts us the most and is easier to hit than the defender" guy standing close to the enemies with a weapon that provokes opportunity attacks.
Even when picking the Archer Fighting Style, I am much more likely to get use out of Running Attack (MP2) than Prime Shot.
Regarding the flanking resource sponge (beast), they are really cheap to res if they die. So cheap, in fact, that we would let the cat die rather than waste a healing power on it. (Of course, our ranger was a Beast Master who, upon learning that having your weapon die on you really sucks, retrained away all of his beast keyword powers and focused on the archery side of things.)
As for the Paragon paths being very powerful, I disagree. The power range seems appropriate.
The Battlefield Archer is definitely the strong one here. It has a weak level 11 AP feature, a moderate level 11 quarry power, and a good level 16 feature. The level 11 power is ok, but not anything extraordinary. Considering the restrictions on action point usage, the level 12 power falls short of being overpowered, but it is quite good and synergizes well with the path features. And the level 20 power is nice for it's level, but only because of the level 11 quarry feature.
The Beast Stalker has a decent, but not great, level 11 AP feature. And if you are in a themed campaign, then the level 11 quarry feature could theoretically have decent utility, but that depends on if you convince your DM to build a campaign for you. And the level 16 AP feature makes up for the relative specialization of the level 11 quarry feature. The level 11 power is powerful, but not broken. The level 12 power is a little weak for a daily (but too powerful for an encounter). And the level 20 power is useful if you happen to be in a campaign with frequent solos (I have yet to play in that kind of campaign, so I just can't appreciate this power much.)
Both, when compared to other striker Paragon Paths, are not worth having your primary class feature be a mere feat. And to take advantage of them, you have to build in such a way that you must forgo the broken goodness of Jackal Ploy.

Given all that, I accept that my original suggestion could be exploited. If you could explain how, I would probably even be more convinced.
Maybe that is the problem. I just don't see this huge power the archer ranger has. The things that I thought were powerful (like Spitting Cobra Stance) have mostly been nerfed into dandelion fluff. So what is the uber powerful ranger build? Does someone have a link to it?
Aside from that, what about this as a feature?
Because of your focus on ranged attacks, you can designate any creature you can see as the target of your Hunter's Quarry.
It would be thematic, have the advantage of simplicity over adding a power, and it would be unique. But, would it be broken?