Leopard 2 tanks are fairly competent main battle tanks. The UK made Challenger 2's are the ones that can really go toe to toe with Russia's T-90s..the problem is that Ukraine is not trained to deal with the maintenance and fuel requirements in dealing with the M1 Abrams and Leopards versus those Russian/Soviet made T-72s and few 90's they have. It's a stalling tactic until they decide the best way to get some planes on the ground for the Ukrainians to use.
Russia has air superiority over Ukrainian air space. They don't even need to engage Ukrainian/NATO forces directly.. acquire target and bombard to all hell. There's really no point in sending tanks when the Russians are just going to turn them into molten steel..Ukraine needs JETS. That's the TURNING POINT. If Ukraine gets a hold of some F-16's, Super Hornets, etc..then I think all of it goes to hell. Those jets I mentioned CAN get in range relative to Moscow..very dangerous game we're playing. And I'm hearing they've begun training remnants of the Ukrainian military who're familiar with flying old Russian/Soviet Sukhoi jets to get familiar with the F-16's systems. It's only a matter of time.