In the prescriptivist lessons of my primary school in the 1950s we were taught that it was correct to say (for example) “He’s better than I” because this was the elliptical shorthand (though that was not the expression used) for “He’s better than I am” — even though none of us spoke that way. We’d say “He’s better than me” or (more likely) “I’m better than him”.
A precocious pupil might have replied that prepositions (“than”, “from”, “between”, etc) are followed by the
accusative case, because prepositions as well as verbs have objects.
So it can be argued either way. But shouldn't normal usage have the casting vote?