It's a new model in so much as it's a model update for the expansion as a whole. Horses as a beast model are used plenty throughout BfA and every unarmored horse model is updated in the old world as well.
It's a new model, but there is no indication that the new horse was specifically made to be a mount for players, and the armor is also ripped off previous mounts. Whereas the Mag'har Wolf model, so far is literally unique to the Mag'har Wolf mount and also has unique armor.
Blizzard mostly focuses on two types of mounts nowadways. 1. Store mounts. 2. Recolors. Once per expansion you might get a mount that looks somewhat new, but they will make a dozen recolors one or two expansions later.
I guess I'm the only one who actually likes the horses. It's gonna be awesome riding around with Warfront Armor and a horse instead of glowy spike armor and a dinosaur.
Seems like a missed opportunity. Could have given the Kul Tiransso something unique and oceany or like a kelpie if it must be horse.