Nonsense. Have you seen Mariupol? It looks like this: https://twitter.com/DPiepgrass/status/1507057301181517831

Officially, as of 9 days ago, 2,400 civilians had been killed, but this is said to be an underestimate and the actual number in Mariupol may have been as high as 20,000... nine days ago. https://www.nytimes.com/2022/03/15/world/europe/mariupol-death-toll-ukraine.html

I know of two factors creating an appearance of "gentle" air power. First, Putin thought he would overthrow the government in three days and did not plan for a prolonged invasion. This is abundantly obvious if you read the history from the beginning (see e.g. the feed at https://twitter.com/WarSignals, from superforecaster Clay Graubard who predicted the invasion, or watch this panel of war experts: https://www.youtube.com/watch?v=zXEvbVoDiU0&t=1474s). They captured Hostomel airfield, then lost it again. Eventually (after you wrote this) they did increase the amount of air power: https://www.washingtonpost.com/national-security/2022/03/22/ukraine-russia-air-force/

Second, the Ukrainian military has plenty of MANPADS air defense systems, so the Russians are losing planes regularly.

Putin has not committed all available forces and firepower to Ukraine. I believe this is because he wants to hold some forces and firepower in reserve in case the war broadens beyond the borders of Ukraine.