Starting next raid event (Sandalphon), BP costs get adjusted to 2 for expert and 4 for ragnarok.

Strictly speaking, Jormungandr isn't the only eidolon with a -10% atk debuff. Yatagarasu should also have the same effect. Yatagarasu's event is 3 months away; so there's about 8 new events plus the 1st reprint before then. So you still want Jormungandr anyway.