Hmm, that’s possible, but given that both Myron and Hamanu are numbered 4th I don’t think it’s just the order the Wanderer learned about them. But the Champion list we’re given being an after-the-fact thing is a good idea. That would absolutely leave the option for a number of other Champions elsewhere.
Yeah, it’s entirely possible that the Crimson Savanna was badly damaged during the Wars and has recovered in the 2000 years since, while the Tablelands have continued to accumulate damage … with the largely scrub-plain Hinterlands in between.
I do think “there were never wizards here on any significant scale” was the original TSR intent, but that’s not required by the material.
Number 1: Fairly plausible
Number 2: This is pretty definitively the case, and they settled there both to be near in case Rajaat gets free, to monitor the Pristine Tower, and because Borys wanted them close. There is no reason to assume the Champions didn’t know the wards would need fueling beforehand, and the other major factor is that the Tablelands have among the most stable, productive, and advanced societies on Athas (also the most populated, hence where any ruler would seek). Plus several maybe even the majority of the champions are also from the region originally.
Number 3: There could be some failed ones out there, or supposedly dead ones that fled to an outer region, but yeah the lore doesn’t really leave a ton of room for more champions
Number 4: There is some truth in this, in that it wasn’t just one big long war, but rather periods of greater and lesser conflict that did become greater over time. There may also have been any number of smaller species annihilated that were not explicitly set out as one champions main perogative