三人行，必有我师(焉)

I'm half-convinced this is also because 粥 itself is literally different per region??

Ah, I hadn't even thought of that. Yeah, I can imagine that if in some regions it's more watery and soup-like, by analogy it would make sense to use 喝 there.

I'm firmly in the 吃 camp, standard-correct or not, and 吃粥 / 喝汤 is what I learned for Hokkien too!

That does make the foreign-influence theory seem less likely! I'd be surprised if Hokkien, Cantonese, and Mandarin all brought in 吃粥 from outside...