I am sure that a long break will not be comfortable enough for players who are used to playing with short breaks. By playing, they actually maintain their fitness. With a long break, players should do their own training to keep their stamina up.
And actually, something that is an advantage for teams participating in the Club World Cup. Especially those who have new coaches or new players who can be played. So each team can prepare for the tighter competition next season.
The break will help the players rest because at some point it is important they take that break, teams who are not participating in the club world cup has the advantage of resting till the next season, they will also be having their personal training because they know they have to keep fit till the season starts and I agree that for teams already participating in the club World Cup it becomes an advantage for such players as they do not have to bother about training to keep fit because they get fit training for their fixtures already, in the next season but I believe even teams who are not in the tournament will still get preparation to staying fit.