2)He exceeded the limit a long time ago, as Brain of Morbius showcases other incarnations of his.
Except, again, that's an inconsistency. "The Three Doctors" had already explicitly stated that Hartnell was the Doctor's earliest self; the Time Lords referred to him that way when they summoned him from the timestream. So "Morbius"'s portrayal of pre-Hartnell Doctors contradicted what had already been established -- and what came later, since there have been multiple subsequent references to Hartnell being the first, either directly or implicitly. For instance, in "The Five Doctors," the First Doctor called himself "the original, you might say," and in "Mawdryn Undead," the Fifth Doctor said explicitly that he had regenerated four times only.
So it doesn't make sense to pick out the "Morbius" reference and claim it's proof when there are dozens of other references that explicitly, consistently contradict it. It's the exception, not the rule. Yes, DW canon is a mess of conflicting references, made by many different people who generally assumed that earlier serials would be lost or forgotten and that they were free to ignore or reinterpret them at will. Generally it's best to recognize that and not get too attached to any one claim or interpretation to the exclusion of others; we should acknowledge all the contradictory information. But in this case, the evidence that Hartnell was the earliest Doctor is abundant throughout the series, and the "Morbius" scene is the one and only thing that suggests anything to the contrary. It's not enough to tip the scales measurably away from the interpretation that Hartnell came first.
