have never seen that spec'd - have never been concerned with the amp rating of a stock ignition switch, especially with respect to just starting and ignition, which GM designed them for - ditto for the generic cheapies, one of which has been starting my forklift for ages
if you have everything wired correctly those simple circuits will not cause a stock switch of any year to burn out, maybe you're putting the actual starter load thru the switch rather than just the solenoid activation?
Bill