Absolutely true, the oil is helping Russia a lot. It probably benefit Russia about as much as foreign aid helps Ukraine.
But the oil can only do so much, when the economy is overheating badly.
The problem in Russian economy is not shortage of money, it's lack of production capacity, and lack of workers to increase it. Probably also lack of ability to import goods like they used to. This puts extra pressure on their home production, and helps prevent the Russian economy to keep up with the increased strain from the war.