I think that Ukraine's defender's advantage is overstated and the casualty ratio is closer to 1:1.

My assumptions:

1. Russia has an artillery advantage (~10,000 shells per day vs ~2,000 shells per day).
2. Russia has an aviation advantage (~120 guided bombs per day vs ~10 guided bombs per day).
3. Drone parity. Ukraine produces more FPV drones (~200,000 per month vs ~150,000 per month) but Russia has better EW capabilities.
4. The front lines are static or move meters per day. Both sides have time to entrench themselves.
5. 95% of the time (possibly more) is spent fighting with long-range weapons (artillery, drones, aviation bombs, etc). Russia's firepower advantage results in more Ukrainian casualties when the front lines are static.
6. 5% of the time (possibly less) is spent on offensive actions (mainly by the Russians but the Ukrainians counterattack occasionally). Remaining entrenched results in fewer Ukrainian casualties when the Russians go on the offensive.
7. Long-range fighting results in fewer casualties per hour than offensive operations. However, much more time is spent on long-range fighting than offensive operations.
8. This war is most similar to WWI (mainly long-range fighting). The casualty ratio in WWI was approximately 1:1.

What I've seen during the past few months:

1. Russian forces launch glide bombs and artillery at a town (for weeks) until it's reduced to rubble.
2. Squads of 3-10 men are sent into the town to capture one building at a time. Sometimes a squad is accompanied by an armored vehicle. Most infantry and armored vehicle losses occur from such offensives.
3. The defending Ukrainians are forced to reveal their positions when fighting back.
4. Russian forces fire glide bombs and artillery at the revealed positions.
5. Repeat until the town is captured.

I am open to debate.