As if coaches of Serie A sides sit there and think to themselves 'gee, I better not rest my stronger players for our game against FC Neverheardofyouandreallydontcare, because we have a more important league match this weekend, I have the UEFA co-efficient points to think about.' They only care about keeping their job, that's doing well in Serie A.
Serie A >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Europa League.
UEFA Cup 10 years ago >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Europa League.
You only have to look at lineups. Look at Spurs. Look at Birmingham City, a Championship club changing 7 players for the Europa League!
First and foremost for them is getting promotion.
But sure, Serie A sides are weaker, that goes for their rotation and backup players.