I have a foldie which recently seemed a bit harder to pedal. Specifically back pedaling seems harder than it should be (if I kick the pedal back, it barely travels a quarter or half turn. I noticed that if I push the bottom jockey wheel up a little, reducing the tension on the wheel, the backpedal test results in 2-4 times as much travel. This problem is also only pronounced on the lower (bigger sprockets) gears. I recently detached and reattached the RD, to install a derailleur guard on the wheel, and subjectively it has seemed different from that time, though objectively I have checked a few times and it seems installed correctly. I also have a squeaky chain lately which I believe means it needs to be lubed, which I am going to do over the weekend.
TLDR: Does the dry chain explain why the back pedaling seems so bad? Is it a matter of lubing the RD jockey wheels? Or is it some other issue. I also see some rust on the RD springs, not sure if it has any effect.