I did a lot of content with rng/clr/brd at 65 and it worked great. I suppose an SK would have been plain better than the ranger in every way, but the ranger is totally fine. Switching in BST is probably very similar. Your rough time (I think all trios have one) is going to be stepping into PoP and trying to tank that stuff with your undergeared BST or RNG. That's going to hurt. It will get a lot better with gear/AA.
I suppose the numbers are objectively known, but but given similar gear and AA for each I didn't feel like the gap between meleeing and shooting was large enough to use a really inferior tank like a shaman just so the ranger can shoot. Double seems high, but I could be totally wrong.
Trio BoT wing bosses with a pre-VT or ele BST tanking seems really optimistic. I think you're going to top out at XP mobs in PoP unless you raid and overgear it. But like someone said, that's cool. Find a friend with a beefier tank and you'll be in good shape. If you're into going out and seeing what you can kill having a group with two clerics is usually optimal anyway, so it won't be a problem if the other person has one too.
IMO people make way too big a thing out of the difficulty of double melee. You just pull mobs to camp and it's fine. Leave one (or both) in place, pull everything to the same spot right in front of them, /assist. You don't have to chase things around if it's all snared and everyone is in melee range.