Arabs and Iranians would most certainly not unite politically due to their historical grievances, pride, competitiveness, and a host of other issues. The Saudis and other Gulf countries enjoy the benefits of allying with the U.S., which they consider crucial to their success. In contrast, Iran is crippled by sanctions that have hindered its economic growth, yet these same sanctions have spurred the development of a defense industry that it likely wouldn't have prioritized otherwise. The Saudis and other Gulf countries will never achieve a military edge over Iran; their best option is to leverage U.S. support against them.
Mohammed bin Salman sees Iran as a military threat and desperately wants to be the only power in the region. He would love to see Iran weakened, as its influence complicates his ambitions for the region. The Sunni-Shia divide further complicates any potential unity, which is also used to inflame the divide for political reasons. It would almost be a miracle if they were able to put all their differences aside.
It’s nearly impossible for the Saudis or any other Gulf countries to unite with Iran politically, as few have the ability to put emotions aside. Of course, for the reasons mentioned above, it's also not so attractive and not worth the problems that come with these sorts of alliances financially. It would also take a lot of stepping on the toes of other allies to make such a power move

you'd have to be free and not a slave to do that.

If such unity were to happen, though, it would require them to sacrifice their relationships with the West, a prospect they would never entertain, let's be honest here, maba ku dhacaan.
I saw some reports circulating not too long ago suggesting that Salman is quoted as being indifferent to the Palestinian issue; it’s not hard to see he's doing all of this speaking up to calm tensions. Many regular Saudis care strongly about the Palestinian issue, and throwing a bone here and there buys him more time.
And if the U.S.'s number one ally sets its eyes on more territorial gains, there’s nothing the Saudis could do about it. Saudis and other Gulf countries are not truly seen as equal partners, nor are they perceived as competent potential enemies that could be a great threat to their number one ally.
I’m sure you have seen the video of Trump saying that he told the Saudi king they would not last a week without U.S. support and that they would have to pay up—they don’t hide how they see them. Can you imagine any U.S. leader saying that to their number one ally? I would not be surprised if a U.S. president were forced to step down for such a comment.
It has been hammered into their heads for decades: enjoy your wealth but do not ever think you have more power than you do; know your place. The U.S. understands this very well and continues to leverage it, deepening the divide between rich Arab countries and other players in the region that could also be a threat to their number one ally. Keeping all sides divided and turning them against each other is a good protection for their number one ally. Unity, however, would be too destructive, and they know this, which is why they have invested so much into dividing everyone in the region.

The U.S. is always ten steps ahead; they have put in decades to make sure such alliances don't emerge.
The Saudis and other Gulf countries find themselves in a position with few choices. If they want to maintain their power, they must be subservient to the U.S. They are constantly humiliated and reminded of how weak and incompetent they are without the U.S. I’m sure they are shown replays of how it ended for Muammar Gaddafi to remind them this same thing could happen to them if the U.S. decides to pull the plug on them in case they forget who is in charge.

When the Mahdi comes, he will cleanse the Arabian Peninsula. He will also be fought by some Muslims. I'm starting to wonder, what if these Muslims who will fight him are Zio Muslims? Allah knows best.