This is "normal".That was quick
Russia outnumbers Ukrainians air and naval crafts by 12 to 1 or something. And they got massive experience from the wars with Georgia, and in Crimea and Syria. Ukraine was always losing there so Kiev could "fall" fast indeed but what would it mean ultimately as Russia wouldnt be able to hold it ? Imagine being a foreign soldier in a city of 3 million where all the men aged 18+ hate you and are potentially armed
Time is against Putin, whatever goal he has, he needs to succeed quick.