Jack's Hybrid look ass and a Hybrid Form combines the Human and Animal Forms to increase Physical stats. Jack's ''Hybrid'' doesn't even effect his arms with which he attacks, they are simply human. So based on paper his attacks shouldn't even get stronger in this form. Having 4 legs is useless, it doesn't make you faster and a trunk in a sword fight is counterproductive, it's just simply gonna be in the way.
I hated BM's Hybrid form mainly because of the weird face it had for some reason, it made her look like a Smile user than an actual Zoan user. Her form is also only a thing, because Oda wanted to go with the whole Yokai theme. Unlike with Jack's Fruit, having only the lower half transformed here is stil usefull at the very least. But i have wished for a more menacing look for her DF in general.