That's still upper-low end. If you think about it, the team is playing 40+ games, in a sport which is 11-a-side. 18 players being used more than ten times is getting towards the low end.
By comparison in 2012-13 it was 22. 2013-14 it was 21. 2014-15 it was 23 (would have been 24 without Romulo's injury).
For interest, other teams last season:
Chelsea (19)
Man City (20)
Barcelona (21)
Real Madrid (21)
Arsenal (21)
Man Utd (23)
Bayern (23)
Depth
By comparison in 2012-13 it was 22. 2013-14 it was 21. 2014-15 it was 23 (would have been 24 without Romulo's injury).
For interest, other teams last season:
Chelsea (19)
Man City (20)
Barcelona (21)
Real Madrid (21)
Arsenal (21)
Man Utd (23)
Bayern (23)
Depth

