I have never had a problem with any of my GM rims, including the original Magic Pie that I unfortunately stress cracked in a few places myself when I attempted to forcefully realign the spoke holes while carrying out
the flange modification by bending the rim with a metal rod
(screwdriver shaft) to make the holes align in the correct spoke direction to alleviate the bendy spokes:
The few cracks that I caused are no worse today than they were over ten years ago and the rim is still straight and true with no loose
(or overtightened) spokes.
I ended up having to replace the Rim for my Magic Pie 5 kit, as my bike guy is saying because the spokes where so tight that you couldn't loosen them. It put pressure on the rim and has cracked it on the spoke holes.
Was this the same bike guy that fitted all new spokes and nipples
just over six months ago?
Spokes do not simply tighten themselves, so they must have been overtightened by your bike guy when he originally installed them.
The main reason for using those thinner gauge butted spokes is to reduce the stress being exerted upon the rim, as the thinner spokes are able to stretch more under high shock loads rather than a thicker spoke simply transmitting the shock directly to the rim. If the spokes are overtightened, they basically lose their ability to stretch and absorb the additional shock loads.
Alan