Here is a different take on this price war from South Front.
It seems that initially SA wanted to cut OPEC oil production to keep the price of crude up but Russia refused to comply and this prompted the price war. This would have the advantage of harming both Russia and Iran and increasing the Saudi share of the market.
But I am not convinced that this analysis is correct for the reasons you state. I am sure that Russia can stand a lower price than KSA and I am not sure that KSA would necessarily have the blessing of Trump to continue this measure which would certainly harm the viability of the fracking industry. If the South Front analysis is correct then it is likely to backfire in the long term in my opinion.