It's not. Surprising fact, but Russian gas supply is 6.5% of primary energy in the EU, and Russian oil supply about as much. It is the largest supplier, but not dominant, and can be cut out quickly if needed. Only Slovakia is heavily dependent on Russian energy, the rest can do without in a few years if needed.

Dropping that much supply in price-inelastic fields like energy is a pretty big deal.

With Iran oil embargo, world dropped about as much (in oil) as Russia exports. Did not prove to be a big deal.

My mistake here. Russian oil exports is 2x Iranian.

Poland s also depending on Russian natural gas (primary source of natural gas in Poland)

Poland produces itself over 70% of the primary energy it uses. So it's not much import-dependent at all. But yes, since most of the energy it produces is coal, it imports about 2/3 of the natural gas it uses, and most of that, about 1/2 of the total use, from Russia. Anyways this isn't a big deal since it has sea gasification terminals, and gas market is going global because U.S. needs ways to export lots of cheap natural gas they have. Right now LNG is cheaper than Russian gas.