Don't see why the scope base screw size would be an issue - they give you an EGW rail with the rifle so it's not like you have to find a base that will accept the larger screws. Aside from that your other complaints are warranted and mimic my own in my review of the Stealth.

As for the accuracy, you didn't state how you are shooting. As you shooting off a bipod or front rest? With or without rear bag? If off a bipod, do you have anything between the bipod feet and the bench? (foam pad, piece of carpet, etc)

Have you tried playing around with the action screw torque?

Have you checked to make sure the scope base screws haven't worked loose? (this happened on mine)

How frequently have you been cleaning it? Some barrels shoot much better when they're good and dirty rather than squeaky clean.

Just some things to consider and maybe experiment with before you make the decision to sell or invest in an aftermarket barrel.

Also, have you tried the match ammo at 200 yards or further out? It's not uncommon for longer high BC bullets to not group as well at 100 yards as they do at longer ranges as they haven't fully stabilized and fallen asleep yet.