I do blame it on injuries. Injuries to Laporte and a lesser extent Stones.Although I haven’t looked, statistically you are probably correct. The thing with Liverpool though is that as long as their spine is intact (Alisson, VD, Robertson, TAA, and the front three) it doesn’t seem to matter who else they lose. Apart from losing Alisson for a few games it has been pretty much there are season. In comparison we have consistent problems at CB and LB. maybe our problems are more to do with loss of form from certain individuals rather than injuries?
In terms of total days lost to injury, I haven't seen the stats, but Liverpool and Man Utd have lost a lot more players but as you say Liverpool have handled it. I think their defence would be wrecked if they lost Van Dijk. City handled losing KDB last season. Some players are key to every team as no squad is perfect.