During Prophet Mohammad (s) time there was fake Prophet Musalyma. He had followers too, but, people (over all) did not take him as serious as Mohammad (s).
That said. We have to also recall some things.
Arabia worshiped Satan explicitly outwardly manifestly. To them, Satan and his forces were the True Angels, while Gabriel and Michael deceivers.
They accused Mohammad (s) of being either (1) a Sorcerer or (2) Possessed (and the miracles hence performed by evil Jinn (accusation of Gabriel and Michael and Angels under them))
When there is miracles in the open, the trial is different. A lot of Quran is about proving why miracles are a proof. For example, 19 Angels guardians over hell, is to emphasize, if miracles are not a proof, then hell-fire and heaven are not a guarantee of justice, but rather, you can be at the mercy of misguided forces that put people in hell forever and heaven forever, and so miracles have to be accepted because they display a power from God that is part of how he establishes the order of the heavens and earth.
A lot of Quran is just about proving miracles are signs of God and his religion.
The Quran is sufficient sign, but it can be distorted, misunderstood, and overwhelmed with sorcery and falsehood.
Therefore much of Quranic arguments condemnation of disbelief is on hold now.
We are more a kin to the period where truth is not manifest, but rather, Satan has upper word in beautifying falsehood and lowering the pure blessed word of light from God.
There is four complaints:
(1) No more Nabi after Mohammad (s) (God stopped talking to us and clarifying in real time what to do)
(2) Hiddenness of the Imam (Imam Mahdi (a) is not in public)
(3) The trials and tribulations of our times
(4) And the numerous number of enemies against us
Shias usually are aware of 3/4, but 1 is also a huge trial. God not speaking to humanity in real time, is a huge trial. In the past, Prophets were succeeded by Prophets and has God communicate books as proofs from him, constantly, and spoke to humans in real time.
This ceased with Mohammad (s).
But the reason it ceased, is part of an elaborate plan, that includes the Quran of Ali (a) which will show the wisdom of why Quran was revealed slowly all over the place and how the Sunnah complimented it as it was dynamically built, and the way Sunnah illuminates the Quran will be a sign for the Mahdi (A) aside from miracles he will perform.
If Imams (a) were Anbiya, there would dispute as to what constitutes books from God, and then this would lead to division and the prestige of Quran would not reach it's status as it's studied today.
This was fine in the past, but not as final plan, to bring Islam to a world stage, and finalize the trial. The Quran thus was designed in a way to apply to all times, while this was never the case with any revelations in the past. They were more explicit and relevant to limited time and not written for all times.
Thus the wisdom of ending Nubuwa you have to understand the Imams and the Mahdi role with the Quran and the Sunnah.