Yes and NO
They face a weaker league if they stay in the same league, the teams coming up are not as good... by staying one extra season in the same level you have a chance to develop your players, so if your players were 5 stars byt the first season - they will be at least 6 stars by the second season in the same level. Example - the guy i'm facing in my league has World Class and Super Stars players at the start of the season, and now after 20 days he has Legend and more Superstars players because of the training he used all season.
As a matter of fact I'm thinking I should stay one more season in the same level but is too late now - I'm second in the league just 1 point behind the leader... if he draws one more time I got a big chance to win the league.
Maybe on level 8 if I get a tough league I will stay 2 seasons... I shall see how it looks first.