Of course, Ukraine is a third rate army, so Russia, a military superpower, should be confident to brute force it if necessary. That was never in dispute, they will eventually win militarily, just takes slightly longer. Their initial original objective was a quick negotiated settlement with a blitzkrieg to surround the capital and hope it sues for peace, that is preferred to maximize gains and minimize cost to Russia lives and economy. A war of attrition is not necessarily inevitable, Russia could have scared Kiev into submission within the first week or so. A war of attrition is the least preferred because the point of a Military Superpower is to intimidate smaller powers before invasion or very early phase of invasion to capitulate. When you have to grind your enemy into ashes/rubble, then you will win, but at a higher cost to economy, causalities, and domestic support compared to a quick negotiated settlement.