If you are punching I'm pretty sure you will want Combo, it will stack with Boarding Up and can boost the damage of your Shield Bash significantly.
Shield Bash works much better against armor compared to fists, you can go from doing almost 0 damage to doing very good damage. You probably want to boost that even further.
I ran this fist+shield build on Hard and it went well, but its focus is somewhat different, less raw power and more crowd-control.
Unarmed 4 AP punches while using heavy riot gear with a tungsten shield, constantly triggering the incapacitate from Cheap Shots, stacking Boarding Up and Combo very quickly, and relying on buffed Shield Bashes instead of Expose Weakness for dealing with armored enemies.
https://underrail.info/build/?HggPBwQDAwYAWgDCoAAAwqAAZDIAfX1Lc8KCAAAAAAAAZCQxwoIgBsKowqoHS8KrT0VGDsKpwrN4beKhkALip4IB4qe-AeK2tQLitrYD4ra-Bt--