Is what Kaibara said about beef being better from female cows correct, though?
A good question. Most of the information I could find is anecdotal and comes from people in the beef industry, but the notion of 'better' feels so subjective, I wasn't sure how to approach it.
So I'll just explain what I've found here.
Generally, the difference in flavour between cow beef and bull beef can be attributed to the different hormones affecting the muscle structure. Higher testosterone levels are often considered bad and contribute to tougher meat, so many places around the world prefer cow beef. Veal is prized even more because calves will not have matured enough to produce these hormones, so their flavour is lighter and less 'beefy'.
Steers, castrated bulls, also won't produce the testosterone, so they are less active and therefore have fattier meat. But, they lack the estrogen that cows have, which I dunno, I guess that's more preferred for some reason?
Even among cows, Kaibara specified they must not have given birth. These are known in the industry as heifers, and their meat is prized for not having gone through the stress of giving birth.
Ultimately, I'd like to remind that these are all anecdotes provided by industry professionals, rather than scientific studies, though for something like this, perhaps that's good enough.