Quite interesting. In old times( well, 30, 40 years ago), I remember, beetpulp was ADDED to the ration in winter ti give a little "juice", much like carrots, since winter means no grass. Nobody would feed beetpulp only, or in summer. It wasn't seen as a hay substitute at all.
I used to add a handful to the feed, in winter, to make supplements stick.
I noticed my horses getting tired of it after the initial joy, unless it was the molasses-added beetpulp.
My landlady, some years ago, bred QH. I did the feeding, formulating a ration for her then just bred mare, the resulting filly won the futurity. She re-bred the mare 4 times to the same stallion, feeding her ration, not mine( consisting of a 10 liter bucket of beetpulp and oats, twice a day), and NONE of the foals ever even made it in the regionals.
Si, I can easily do without beetpulp. I also read beetpulp can be high in aluminum due to processing with solvents in metal containers.