Thanks for your advices.
After reading your reply, I just notice my same level (Level 25) friends have been dropped to 3 only. But none of them were grouped to the same league with me. Differences in qualities might affect drawing. To prepare for next season, I will try to find some new Asian same level friends now.
You are wise to know that this is the result of drawing being affected by time zones of opposite teams. This is reality that I understand.
I am still proud that my 35T teams are still competitive and never failed to promote. But it is true that they may not be the title contender in every season.