That's pretty poor, my 147 is equipped with a standard setup and whilst it's a bit over-braked, it's saved me from a couple of smashes in the past.
I'd get the whole lot stripped down, have the servo checked or replaced for a known working one, likewise the master cylinder.
See if you can check what pads were last used by your mechanic and if they're a no-name POS, then bin them and upgrade to some performance ones.
While you're doing it, have the calipers cleaned, greased and freed if sticky, and new brake fluid, which you'll have to replace anyway if you remove the master cylinder.
Don't bother with upgrading the disks