I remember when the "counteroffensive" smacked against the Surovikin Line, and Russia MoD posted some numbers for casualties. A navalnite lib I know (from waaaay back) mocked it, smugly asserting that the ratio was greater than the one at Omdurman.

But I guess this 7:1 idea is fine by them

Not really. The relevant metric is “combat power”. If the attackers out number the defenders or if the attackers have more big guns and more ammo than the defenders then the casualty ratio can be much worse for the defenders.

Russia likely both outnumbered the Ukrainians in the sector and even the Ukrainian side described Russia as having a 5-10x artillery advantage, with Russia saying 10x.

Under those conditions the actually observed historical casualty exchange ratios in modern battles would suggest significantly worse casualties for the Ukrainians despite being the defenders. Possibly even much worse casualties with some battles from the US experience in WW2 and Korea said that with sufficient “combat power” they documented even a 5:1 advantage for the attackers.

Most battles see defenders and attackers taking roughly equal casualties in fact.

http://www.dupuyinstitute.org/blog/2018/03/05/comparing-the-rand-version-of-the-31-rule-to-real-world-data/

Part of the reason for this is that basically defense isn’t a static thing. Defending a place actually involves going on the attack as well. You don’t just sit there and wait for the enemy to slowly roll you up, you have to hit back to disrupt his plan. Defending in modern war actually involves a lot of attacking.

Also the attacking force has the initiative. They can choose where they want to attack, from where they want to attack, and when. The defender is forced into a more reactive role.

Given Russias large combat power advantage and given that Russia had the initiative and so was able to partially siege and take its time with the attack to maximize strategic advantage, and given in the end it became a disorganized rout, actually you’d expect Ukraines losses to be probably worse and possibly a lot worse.

No, being dug in in a battle where enemy have significant artillery advantage can cause 7 to 1 but the 7 is lost by defenders. Compare for example with US battles on the Pacific, where Japanese were heavily dug but still took many times the losses of attackers despite the attackers using infantry pretty actively and aggressively too.