No, i was mid table in my Gold Division when i got promoted to platinum. I think, when battle.net thinks you're ready, the server will match you up constantly against players above your rank. If you're platinum you'll play against diamond, maybe up to 6 or 7 straight game. It doesnt matter if you lose 6 straight game, you'll still be matched against diamond players. During this period you need to get 1 or 2 win to get promoted. My friend just got promoted to diamond league today. He was losing 6 straight match against diamond players, then on 7th match he won and got promoted.

a few matches for u i bet will land u on the diamond league. Wins of course..