MLB Hero Elly's Adventure vs. MLB Limited/Zero Over

AFAIK, it's multiplicative, but yeah it's stronger than LZO in terms of NP damage either way. If making the NP stronger is your main concern, then Hero Elly is a good choice. Of course, your regular buster cards won't be as strong, so whether or not it's worth the trade off really depends on the servant and the situation.

IMO you should put Elly on servants with QAABB deck (Altria saber, Altera, Jeanne alter etc)
and LZO on servants with QABBB + np B deck (Ibaraki, Kintoki berserker, Gawain etc)