Slugging is not a parlor trick at all. If dealing with an older firearm or war time production, it is perfectly valid. A gun can go from 10" groups to 1" groups by sizing bullets to bore. It helps greatly with leading problems on revolvers. A made in the USA barrel, any time in the last 15 years, slugging the bore would be the last thing I would check. And, only if it were a valuable item. Will a $22 barrel have looser tolerances than a $300 premium barrel? Absolutely. The $300 will have a perfect crown, no burrs in the ports, concentric chamber and bore, polished feed ramp, tighter lock up, etc. The $22 barrel will probably have tighter tolerances than a 1900s Colt but it won't have all the finishing touches. The last 2% is 98% of the cost. You won't see chatter marks in an expensive barrel but beyond fouling faster, chatter marks are not going to hurt much that can be observed in a pistol. Bench rest shooters where matches are decided by a tenth of an inch, it matters.
Sadly or luckily, however you look at it, a new barrel is cheaper than all the gear to slug a bore. Let's say slug it and the bore is oversized. You have to decide if you want to order specially sized bullets for that one gun, reload for it, keep that ammo segregated and make sure you don't feed it in other guns. Would I do this for a parts matching pre war Luger? Absolutely. Is it worth it for a modern 9mm when you have several to feed? Not really. Buy a different barrel from a different manufacturer and see if it tightens up. Preferably with the fewest add ons like porting as possible. You have a problem child, eliminate as many variables as possible. If you want a ported barrel, research who does porting correctly and pay up. If it turns out the iffy porting is the cause of inaccuracy, well, you have proof in your hands that it is true.
Regarding the crown. The crown is the last thing the bullet touches on its way out. The crown is only as good as the last time it was inspected and nothing touched it. It could easily get a ding sitting in a range bag. The different crown shapes and angles help to prevent damage but damage is always a possibility. Just because it looked good new is no guarantee that something didn't get to along the way. A burr in the porting is going to scrape the bullet and change the diameter right before it leaves the barrel. It will have less of an effect than a damaged crown but it can't be good for accuracy.
