A lot of horses do fine, it is true, on sweet feed, but I feel certain - based on my own experience - that ALL horses will do better without it.
I have fed it, and I no longer do.
I find you can feed less of the non sweet feed type feeds and get a better condition, and I've had some horses that just looked like death on it, and when
I changed the feed, their condition changed only for the better, but also,
most horses do best on an all hay diet it the hay is good quality and they are lightly worked only.