One major upgrade on the drum brakes if it doesn't have it and very cost effective .. Self adjusters .. They will stop that pull to the side most of the time under braking ..
Could you have a seized wheel cyl. Maybe one side of a cylinder is working but not the other? Just went through that with the wifeys van and her peddle was good to, but crappy for stopping. Found driver side cyl was stuck solid on front shoe, and passenger side was leaking, which explains the low brake fluid...lol.
My brake pedal is hard and has low power. L have sanded the shoes, cleaned all the hardware, flushed and bled the lines and adjusted the brakes. Still not as good as I have had in the past wirh other E's brakes. The PO did a brake job on it and parked it for 10 years . I suspect the old shoes that look good. Any help appreciated.