I like rice bran for the fatty acid content (beet pulp has next to none by comparison) and find it more efficient for putting weight on a horse than beet pulp - the latter I would consider if the horse was unable to consume enough hay or the hay was seriously lacking in quality (could substitute or be used along with hay cubes), or if there was an issue with them staying hydrated.
That being I'm used to using beet pulp as a medium to make feed more palatable - rice bran, ground flax, loose minerals, all tend to be powdery and we would mix it in with beet pulp to make it easier to eat. No problems feeding like that at all. I wouldn't consider either to be a "heavy" feed - not sure what you mean by that exactly, do you mean too "rich"? Like a double chocolate fudge cake with the density of a brick is for us?
- you don't need to feed pounds upon pounds as you would with high NSC feeds, and much of beet pulp's weight is water (assuming it's soaked, no experience feeding dry as I don't like to) so I would consider it fairly "light" by those standards. I don't really care for feeds that "fill" up a horse's belly, since being full isn't something they're built for. It's just asking for issues like ulcers and colic IMO.