Thanks for the comments Countjulian --- I'm actually quite surprised nobody seems to have made this argument before, at least that I could find (I wouldn't be shocked to find some scholars have made the same points, I just couldn't find it), and I searched hard to find an example of somebody else who had criticized the historicity of Abraha's expedition, with de Premare being the only guy I found who just straight out rejects it. Interestingly the essay was almost complete when I ran across de Premare's essay, and I'd hoped he would have some great new arguments against its historicity that I could add. But no. He basically just says it's a bunch of legendary bullshit, distinguishes the Murayghan inscription in largely the same way, and moves to textual and linguistic analysis.
You might be interested in this:
Abraha and Sennacherib: A Talmudic Parallel to the Tafsīr on Sūrat Al-Fīl
Author(s): Gordon D. Newby
Source: Journal of the American Oriental Society, Vol. 94, No. 4 (Oct. - Dec., 1974), pp. 431-437
Can't post a link but - (jstor.org/stable/600585)