How do you define a miracle?
A miracle is an act, that can be done extremely rarely. Something that people normally cannot do. For example, in the history, it is said, Moses had a stick which turned to a big snake. Assuming this really happened, it was something extremely rare. Something that normally, people cannot do.
Likewise in the history of mankind very few people brought verses in Arabic, which claimed to be the Words of God. This act is extremely rare, and in fact Since Muhammad, almost 1500 years passed, Only the Bab did the same claim, that is bringing verses in Arabic, and claiming them to be Word of God. You seem to overlook this! Of course there has been many people who claimed to be Mahdi, or a Prophet after Muhammad, but non of them, brought verses, claiming to be the words and commands from God. This is a miracle, since in the history, it happened extremely rare, which is what the Quran claimed, that, no one other than God can reveal it. It is only for this reason that, the Quran is a miracle, otherwise, if many people could bring verses and claim them to be from God, then there was nothing miracle about the Quran.