The brakes have improved considerably with use and feel much better, they are nicely progressive (as opposed to our 2010 Zafira which is shockingly off/on). I have a secondhand servo on the shelf but feel no need to fit it. I suspect a combination of corroded discs and possibly even a seized piston or calliper.
Typically I'm not a heavy braker but I've tried some brisk stops in both dry and wet and the car stops well and nice and straight with no pulling.
It's very satisfying getting a car that was loved but little used back in to daily useable condition.