They could have if Russia was really willing to take the gloves off. To put the "war" in perspective it would be like the state of Oklahoma trying to fight off the entire rest of the US military combined while China and, like, Iran were donating them some money and weapons. Yeah they could drag it out for a while and do some damage, but win? Or even survive in the long term? Absolutely laughable. Russia is bigger than the US and Ukraine is smaller than Texas.