Is it common for the attacking army to lose 3x as much as the defending army?
I assume the much of the Ukrainian tanks and artillery are ex-Soviet and therefore of similar quality to that of the Russian.
As you are aware, the US led allied army in Iraq had very few losses while defeating the Iraqi armed forces both in 1991 and later in 2003. Historically, before the advent of air power and modern warfare, to successfully defeat a defender, an attacker would need a 3x, 4x, or even 5x numerical advantage. Exceptions might include use of special forces and guerilla tactics. Air power changes the old warfare formula. The problem in Ukraine is the Ukrainians are not able to apply effective air power, but then neither have the russians been able to so far.
In this case right now the defending Russians are losing way more than the Ukrainians - mainly because Russia is out of trained troops and new equipment - having to rely on the few trained troops surviving to back up “meat assaults” and ancient vehicles refurbished from decades of open air storage. Most of the critical equipment relies on Western parts which are not available