1. I do not believe there are lots of them running around. We know TARDISes were tightly regulated, and running around the Universe freely was frowned upon while Time Lord Society was existent. So, there wouldn't be that many running around in the first place. And, many of those who were running around the Universe freely would have rushed straight home to join the fight. Someone like the Rani (or The Master if he wasn't enticed by the promise of more Regenerations), would've stayed out of it, and could still be out there.
2. Time-Locked is not dead, it's frozen in a moment of time, or outside of time or whatever, and they've already escaped from it once, and Daleks have escaped from it, so, although an almost inescapable prison, it's not actually DEAD.
3. Yes, I realize the Writers' intent is to remove them from the playing field, but, it's not necessarily a permanent situation, there is a loop hole if they choose to use it. If they really, really wanted them dead, they would have been killed, the planet would've blown up, instead of Time Locked. RTD chose to Time-Lock them instead of killing them, so, they could be played with as in The End of Time (Plus The Master and the Daleks returning)
I think we're talking about different things here. My intent is not to rain on your parade. I you want to believe that Susan or Romana or other Time Lords are still out there, that's of course fine with me.
I don't really care for the in-universe situation, to be honest, because the Doctor Who universe doesn't actually exist. The only things that exist are writers, what they have written and what they intend to write in the future. For now, the Doctor is the Last of the Time Lords. It means that there are no other Time Lords, otherwise what is supposed to be tragic would just be a sitcom-level silly misunderstanding. Clearly, that is not what was intended by Russell T. Davies & Co.
And yes, of course it may not be a permanent situation. Nothing is permanent in serialized fiction. Any writer could bring the Time Lords back in any kind of ways, and whether they're dead or not doesn't change a thing. In an anything-goes fictional universe like the Doctor Who world, nothing prevents anything from happening. But for now, that has not happened, and from the show's point of view, the Doctor is unambiguously the last of the Time Lords, i.e. the only one.