Russia is strong like an ant is strong: strong but insignificant. It only has any significance economically because it has oil and gas.
Russia is fighting its own battle at its own border against an enemy which receives some support from NATO countries.
US leadership fights to not lose face, Russian leadership loses a lot more than face if they back off.
Iran doesn't need to conquer or hold Hormuz they just need it in missile/drone range - it's not symmetric.
As for the impact on the global economy - the entire world is letting Iran hold its gas/oil hostage because of something the US did. I'm not sure why those countries don't pressure Iran more they're not at war with them they shouldn't be embargo'd.
Decimate? Sure. Conquer? Absolutely not.
Iran is a huge country with dispersed command and control and generations of people raised to hate the U.S.
Just war [0] proponents will argue both. For instance, targeting civilians/civilian infrastructure is gravely immoral (the decimation part), but also any armed conflict is unlikely to be successful and thus would be immoral on the grounds that there is no reasonable chance of success (the conquer part). But frankly, in this case, we don't even meet most jus ad bellum criteria, let along jus in bello.