I got the argument from Ismaili

I am not an Ismaili and I am an Ithna Ashari and alhamdulillah for that.

I encountered the argument from one of the Ismailis, of their Imamat. He said during conversation, “When an Imam practices taqiya by concealing his true identity, the entire community does as well.

It is inherently inconsistent to be openly Shi’i while the Imam is hiding. You’re supposed to publicly identify as non-Shi’i until he unveils himself.”

It was intrigued me and I want to know why Imam Mahdi atfs is in ghaybah, not the other Imams, even most of them were brutally martyred and killed by the oppressors. Thank you so much for your answers in advance.