i don't really have an advice but i think that's normal when using pump i remembered having to hand express for 1hr to feel relieved. i only have this issue with my left side. maybe you can try hand express while pumping? i saw a video that shows pump + hand express at the same time gives more output than just pump alone.
can explore Horigen Chicture from ourlittlelamb.com.. it has independent left right suction control.
Having the same problem. Efficiency is low for me. Can’t catch up w baby needs.