Russia is still a country of 145 million people (+9 million in Belarus) and huge natural resources that are in high demand across the globe. That's still enough to be a major headache.
they became increasingly reliant on Russian energy. Shutting down their nuke plants for example.
Natural gas and NPPs aren't really in the same market.
When it comes to electricity, NPPs are for base load, whereas natural gas is for load following. Natural gas can be used for base load, and some countries do this, but in most countries other sources such as coal are usually more economical. One might argue natural gas became more important in Germany because of their ideologically mandated devotion to renewables and shunning of coal, but it is not written in stone that they must shun coal. As we've seen, Germany was perfectly willing to burn more coal when it was judged necessary to do so.
Also, a huge application for natural gas is thermal power, such as in residential heating or in industrial furnaces, and as a chemical feedstock, such as for the Haber-Bosch process.
refuse to submit
That's not being cocky. It's just acting in their own interests and against the interests of others.
They're cocky in the sense that they're willing to do a lot for their own interests even if it goes against US interests. They're unwilling to submit in the sense that they're not willing to let US interests take priority over their own interests.