> Russian budget receives the money in taxes paid by exporters
That is incorrect. The oil and gas companies is owned by a few oligarchies with direct ties to Putin and the Russian government. Based on what secret service and other agencies has leaked, there isn't a major difference between what is the Russian government, what is controlled by Putin, and what is owned by the owners of the oligarchies. To a degree they operate just like a banana republic in this aspect, although a better comparison is likely state owned Chinese companies that get funded, instructed, operated by government personal, given benefits by their secret service, and with party representatives being directly involved in the leader structure and ownership.
And it may indeed take years before the sanctions actually hurt enough for the Russian government to start move to the peace table. American war in Afghanistan took 20 years. Iraq started in 2003 and ended in fully in 2021. Their war in Pakistan took 14 years. Yemen is still ongoing, same in Somalia, and Syria.
6 months would be comparable short, and it is not out of the question that it may take many years. The more funds they get the easier they have in continuing operations. And while Russia produces nearly all of its military equipment, just like the US does, both require a lot of imports to actually do the production. Military equipment require a lot of electronics, much which isn't produced in Russia. Machines, vehicles, technology and tools all depend on international supply chains, and the more isolated the nation is the harder and more money they need to spend on maintaining those critical imports. All while the nations population suffer from the economic downturn. At some point reserves gets low and that is when peace is best pursuit.