I said this would happen a few days ago.
If China manages to reduce American influence in Saudi Arabia and the Gulf, it will only be viewed as a good thing by the Iranians.
Don't count on that, voyager1.
I've previously said that the US presence in the Middle East is a hindrance to a Iran-Saudi rapprochement and peace
US and Iran have long-standing grievances against each other, which go way back to when the US supported the Shah of Iran, who was overthrown because he was seen as extremely corrupt, non-religious and out of touch by the people. This casts a shadow over everything.
But in recent years, US interest in the Middle East has waned as:
1. The US no longer imports oil from the Middle East
2. The US is pivoting from the Middle East to China
3. The US wants to forget about the endless and inconclusive wars in the Middle East
Without US attention and support, this has helped the Saudis realise that its enmity with Iran is counter-productive, as neither Saudi nor Iran are big enough to dominate each other. And yes, the Iranians will be calmer if US influence and presence is reduced in the Middle East.
Just to summarise, a US withdrawal from the Middle East and an increased Chinese presence in the Middle East will reduce tensions and promote peaceful economic development. This is a good thing for Iran, Saudi, the wider Middle East and indeed the world.