I agree with Mearls about the Ranger, it is not a nature's paladin at all. And it is not a half-fighter half-druid either. The roots of the Ranger are in Tolkien since the name itself, and it's got a lot to do with "ranging" i.e. reaching the farthest reaches of the world into the unknown. Being a survivalist and keen with nature is more like a necessity. I don't know where the "defender of the nature" came from but I think it came later, possibly from FR?
I do not feel the same way as his about Barbarians being nature's paladins either however. If they mostly represent the heroes of semi-civilized folks, they might still have more ties to nature than fully-civilized folks in the form of being more dependent on nature (and possibly even having a more nature-based religion), but they might also just be exploiters and plunderers pretty much the same way as city-dwellers.
Ancestral Guardian is a very cool concept by the way, but I do not see how this is more tied to nature than e.g. a Totem Warrior. Quite the opposite in fact, as soon as you're strongly tied to your own ancestors, you are putting your tribe and lineage pretty much above other people and creatures.