The most important thing in the new update...for you?

[Harti]

The leagues are meant to be somewhat sticky, it's not a bug but a feature.

While it is true that it sometimes just feels like ages, it is very hard for a machine to determine your skill without knowing much about you and your opponents. The system shouldn't prematurely assume that you're capable of playing that level and put you into a league where you would get beaten like a sandbag.
I do agree, though, that leagues should be made a little less sticky, i.e. pair you up / down against the respective next tier more quickly, and if you keep having positive records against all sorts of players you should be promoted ASAP.