I think thats kinda too easy for the strange Milken family. I think Dexter expects Tiffany to overthrow him and is disappointed if she doesnt try/succeed. I feel like thats how leadership switches work in this familyI like your interpretation... it brings joy to my Update deprived rage filled heart.
As for Dexter VS Tiffany ... well now that she has power from such a rare and powerful monster and greater support from the MC it actually tilts things in her favor, Dex wont give up control too easily but she is in a position where she could simply be more suitable to be the head of the family. It is possible that if Dexter has the same cold calculating logical mind as her then he might simply just accept her as the superior leader and himself as her subordinate... though for that to happen she would have to even the odds and know all the secrets Dex and HERO have been keeping for decades.
Huh... I am not a member of 2 of those. Maybe 3.
Xanthe told him that Deus said shes gonna kill him and Dexter just replied that deus shut mind his own fucking buisness