I don't think anything should be changed, in the instance of this particular complaint
Basically the OP is saying 'I should be in a league with people around my own quality, who have been promoted from the same level as me the previous season'
Just for a second, think about that. Think about how it would work, in simple mathematical terms. If you're having trouble, I'll tell you - it doesn't work
The number of available players for each league structure based on this little programming 'if' would dwindle to the point that no leagues could be full. And at the higher levels on each server that would happen in about two months
I understand that it must be frustrating not hitting your goals every season (which seems to be: get promoted, have a good cup/CL run). Perhaps you just need to adjust your expectations e.g first season after promotion aim for cup\CL, second season aim for league