That "they didn't have any big cranes" forces the analogy in a way that breaks it. The solution wherever cranes are used is absolutely to get a bigger crane. And also, oxen were absolutely bred to be bigger. That's kind of the defining thing that distinguishes draft oxen from other kinds of cattle. But that process was limited by some factors that are peculiar to domesticated animals. And, of course, if you need to solve the problem right now, you make do with the current state of the art in farm animal technology.

Admiral Hopper's lecture wasn't delivered too long after 1976, which saw the release of both the CRAY-1 (single CPU) and the ILLIAC IV (parallel). ILLIAC IV, being more expensive, harder to use, and slower than the CRAY-1, was a promising hint at future possibility, but not particularly successful. Cray's quip on this subject was (paraphrasing) that he'd rather plow a field with one strong ox than $bignum chickens. Admiral Hopper was presumably responding to that.

What they both seem to miss is that the best tool for the job depends on both the job and the available tools. And they both seem to be completely missing that, if you know what you're doing, scale up and scale out are complementary: first you scale up the individual nodes as much as is practical, and then you start to scale out once scale up loses steam.