It shouldnt be enough - if this would be the case, only one tribe per letter and tribe-sizes ranging from anything between 11 (one nunh + minimal amount of females) to something around 200 (3 nunhs + 50 girls for each + younglings, Tias etc.), we would have lost tribes by now.
I'll bring up a point I mentioned earlier: One of the greatest concerns we're having with endagered species in the real world is that once their population gets really low and is confind to only one spot (like an island, a very specific mountain, whatever - basically that animal only lives in this one tiny place) they're under constant threat to get wiped out rather easly. One storm, one bushfire, one illness, maybe even one predator would be enough to wipe out an entire species. And without another population of that species elsewhere in the world, that animal is gone forever.
Now, Miqo'te arent animals of course, but there are still lots of scenarios that could easly wipe out smaller tribes, like an illness. Think of the black death in europe - or of the Tonberries of Nym, to stick to the game!
Having tribes with such low population, while also still rather living in the wild, being hunters and adventurers does seem dangerously low.
It opens up two scenarios though:
(1) The one I proposed already - several branch-tribes per letter. You'd always have a "back up" tribe, so to speak.
(2) Once a tribe is wiped out, that letter would become free, right? So any Tia could go, gather some girls and claim to be the new G-tribe, after all of its members died.
I have to say that I like my explantion better, though...
And I get that population scale is difficult when it comes to a video game, so I'm not running around in Ul'dah counting the people and going like "Well, 20 people is pretty low as population for a city that I should believe is one of the biggest and richest in this world!" because I can easly convince myself that there are thousands of people I'm just not seeing. They're limited by the enging (and of course, our favorite: The limites of the playstation).
When it comes to the Seekers though, they've limited themselves by lore. If you do the math, according to that lore, you end up with only a few thousand Seekers tops.
...it just doesnt add up if we only assume 26 tribes with 10-200 people in each!
