I've never liked Mags. They always seemed to have problems in the old days with spikes, dropoffs, chops, breaks, leaks, vents, etc.
I saw countless teams loose tournaments because of its notorious spike problems.
But when I look back, I think the issue wasnt so much the Automag, which I admit is a brilliant design. But attitudes towards Co2.
Before the Automag, paintguns didn't have regulators, or sensitive pneumatic components. So they all could run the dirtiest liquid co2, directly into the gun, and it didn't really make a difference.
So, when the mag first came out, owners treated it just like there Tippmanns, Sheridans, and Brass Eagles. That led to all of its problems.
AGD understood this, and pushed for HPA, since filtered HPA seemed to solve nearly every issue with Mags. But by the time there was a sufficient infrastructure to make HPA usable, most teams left AGD for other guns (ie WGP, etc).
These days, attitudes are different. Newer players FEAR co2, so they are far more careful in how the run it with drops, anti-siphons, fitlers, e/cs, lpcs, etc.