Well fact is some countries take much more, Lithuania one of them.
Uk stepping out of the Union would mean the rich EU countries will have a heavier burden. I don't think they will accept that, knowing they already are doing more in the refugee problem.
Let's hope these countries will force the poor countries to donate more or help out more. It's a democracy right?
Your explanation and solution is similar to signing a bank loan contract and as soon as the bank feels insecure or gets in a bad situation you start repaying your loan with much bigger payments than agreed upon.
Joining the EU is a contract - you know the terms prior to signing it. If you do not like how everything is developing go ahead and break it, but do not blame the ones who honor their signed contracts.