1.) You are confusing 2 things:
a) The bonus your arc gives you: This is always +92%
b) The percentage of your guild thread. This can be 90%, 85% or maybe 92% depending on your friend.
Your arc bonus always stays the same. Even if you invest in a 90% guild thread you still get 92% bonus back. Your arc does not suddenly loose 20 levels. If you pay +90% to a friend and get 92% back you have a profit of around 2%. If you invest in a 85% group you will get 7% profit.
2.) I already fixed the recurring quest bug in the beta branch on Github a few minutes ago. We just need to release it. Making a downgrade option just for you will take longer than releasing the fix for everybody.