Molly-FOSS and Signal without Play Services must have battery optimisation exception so as to be able to maintain an open websocket connection for push notifications to work.
Signal and derivatives setup as above will show high percentage battery usage but its a percentage of a whole and just one abstract metric.
You need to balance it off based on functionality provided, time between charges, screen on time, brightness setting etc etc.
Don't just jump to the wrong conclusion over one stat. Take a whole picture approach.
My 6a can get 36 hours, 6-7 screen on time (dependent on brightness) with Signal/Whatsapp battery unrestricted as well as use of everything else I need with switching in and out of my Play Services profile as required.