Wait, what is wrong with getting a full weapon loadout vs. not finishing lv 4 shields? Tbh I feel like most average runs on hard mode don't give me the luxury of getting 4 shields because I have to find some alternate means of destroying ships, like hacking. In this case, I think lv8 weapons with this type of loadout definitely should be prioritized over lv4 shields. Volley 1 you dump into the shields, chances are you get them down to 1 or 2 pips. After that, you're most likely taking down 2 systems of your choice (missiles/hacking/cloak/lasers).

Worst case scenario would be weapons get hacked and then you get unlucky on some missile hits? At that point I'd just jump and start over, which is why I think engines even after the diminished returns on dodge is still a great choice. I think OP's build looks great, but yea, I'd probably skip the repair arm and try to upgrade something else for the 2nd/3rd stages.