I can't say I'm a top level competition shooter, but I have shot in my fair share of big competitions. For a long time I used my surgeon action with AICS stocks and a few different barrels. I also ran a jewel trigger. This rifle was a hammer and I had no complaints with it, until my trigger went down in a match. This sucks when your counting on your rifle to perform.
When the AIAX first came out, I picked one up. This rifle is amazing in every way. To me custom, non custom, whatever, the rifles just dint compair. The smoothness of the action, accuracy, the trigger, ergonomics of the system, and the reliability is just second to none. The rifle is heavy, it's a beast.
Compairing just accuracy, custom rifle compaired to an AI, your not going to see any difference. The AI may even be a bit less accurate. I still wouldn't trade mine. Your right, you don't see many shooters shooting the AI's in comps. I think part of the reasons could be price, weight, and metric threads. You could get a few Remington's put together with custom barrels and stocks for what the AIAW/ AX costs. I for one will continue to use my AIAX in comps.