The thing is because miracles are stuck in the past (except the writing type like Quran), it's necessary that the divine mission be continued in succession of guides that all display miracles.The Bible and the NT are filled with miracles. They do become a big part of what makes the religion true and from God. Baha'is do have an important point about "miracles"... they only are convincing to the people that witnessed them. But that's not exactly true, because we are then expected to trust their testimony that those things actually happened.
And people in a religion, like Christianity, do come to believe that the stories in the Bible and NT are true. I question them. Like a typical one is Jonah being swallowed by a big fish. Or that Moses parted the seas. Or may favorite, Moses' staff turned into a snake.
Great stories. Great miracles. But did they really happen? What's strange for me is that Baha'is downplay the miracles in the Bible and deny that one of the greatest miracles, the resurrection of Jesus, really happened.
But to get back on track with the thread.... The succession of leadership in the Baha'i Faith goes all the way back to you and your religion. Was the Bab the "Promised One", "the Madhi" or whatever he was claiming to be? Then... was there supposed to be two "Promised Ones", the Bab and Baha'u'llah? Then within the Baha'i Faith itself, that's for them to decide, whether Abdul Baha' and Shoghi Effendi and the UHJ are the legitimate ones that were to succeed Baha'u'llah.
The Bahai faith says Bab is the Mahdi, well if it's true, that means Mohammad (s) either had eleven successors or 11 + (Bab + Baha'allah + Abdul Baha + Shokh Efendi) making 15. It goes against the Quranic and hadith number of successors to twelve.