Spain loses a big 20/21 co-efficient year v a bad Italy co-efficient 20/21 year. Italy has 7/8 clubs still in UEFA competitions and has 4 more points than Spain currently. Spain has 6/7 clubs in competition still. The current system rewards multiple teams v 1-2 teams doing really good. This is why Real winning CL wouldn't do as much as previous versions of UEFA co-efficient.
To put that 4 point advantage in perspective, most of the top nations' top years are 19-21 total points. We're talking a 4 point advantage already with an additional club in the competition. Athletic, Girona, Real Betis, and Real Sociedad aren't doing better than Atalanta, Milan, Fiorentina, and Lazio.