A match barrel's improved accuracy comes from:
1) bore machining precision and finish- this allows the bore to keep cleaner
2) stiffness - reduces touch points and makes vibrations more consistent shot to shot
3) mating- A match barrel will have threads and mating surfaces indexed to the bore
4) weight - key to holding steady
5) concentric crown
6) perfect chamber
These things make a match barrel. Reducing weight or not truing the action eliminates some benefit, but not all...