The reason why saudis losing is because of expensive amreekunt trash and lack of army organisation within their own ranks they suffer from terrible attrition within units.
It is more about Saudi military limitations. They are some of the least and ill-trained soldiers in the world. Many of their combatants in the past have been Pakistani troops or hardened Bedouin people rather than the softies of big cities like Jeddah, Dahran, Riyadh, etc. There are several interviews of US Army trainers on YT and other channels who were stationed to train Saudis. They openly say that Saudis are the most undisciplined troops they have seen around the world. Not even the ANA was that bad despite rampant corruption.
Knowing how to fight and having a swanky budget are two different things. There's a reason why the US bases in Saudi are given so much importance. MBS is however playing dangerous politics. He wants to push the US around by ignoring Biden. Given the state of mind American policymakers are in right now, they might just decide to pack and move out of Saudi in a couple of years. That leaves the Arabs at the mercy of Iran.
Iran has a tiny budget but Iranian forces regularly participate in covert operations against Israeli/NATO operations in Syria. They may not have the resources, but are battle-hardened and minus Western backing, will just walk in and take over Saudi Arabia.
Iran-KSA situation regarding weapons is quite similar to India-China situation; one lacks sufficient equipment versus the other lacks sufficient combat capability.