The quality of the weapons themselves isn’t the issue.
Saudis have some of the best weapons around; our weapons. Our tanks, our missiles, our aircraft. The problem is their culture, where the military is little more than a patronage society that doesn’t promote, prize or train competence.
A little more on this here:
Soldier for soldier, the Saudis might be even with the Iranians. But in terms of their leadership? Of their Combined Arms doctrine? They’re ability to respond to requests for strategic munitions deployment? E.g. “I need an airstrike at such & such position at this & this time”?
They’re severely lacking, and there’s little to indicate that they’re improving. Because the Saudis never developed a culture that was literate with technology, or in promoting best practices.
The evidence right now, is that Iran’s strategy of instead emphasizing conventional warfare through hegemony, is working.
Saudis have basically lost the fight in Yemen. They have the Houthis outnumbered, severely outgunned, and yet, they’re steadily losing. It’s the Saudi Vietnam.
Having the Saudis waste billions on weapon systems that produce ineffectual results? That’s clearly a win for the Iranians.
Provoking the Saudis into acquiring a nuke that would make Iran’s “vassals” think twice about fighting the former? It would promote stability, and that’s not what Iran wants in the Arabian peninsula. They want instability that they can seize upon, & promote their geopolitical interests through, if not give them a window to seize territory.