what you say is true, but you forget to understand the reason for this
the Italian championship is very tiring, think Inter lost to Sassuolo twice, a team that went to Serie B
Every game in the Italian championship is difficult and important, you can`t save resources and effort, it could be damaging and counterproductive
so you understand well that it becomes difficult to do demanding things like UCL
I think every league in Europe doesn't have much difference in the number of matches for each participant in the UCL at first. But next they will be different because the strength and ability of each team is different. In every league they don't only compete for the knockout round, so that's why the competition will have many matches. Saving energy with some rotations is necessary, it will keep the players fit in long competition matches. So saving energy can be done by changing 10-20 minutes before the time runs out. I think every coach will do that. I don't think it will do much damage, but it is a strategy.