I think the problem for the Americans related to the weather conditions of Western Europe.
Self evidently the bomb sights they would use, principally the Norden Mod5/M-7, M-9 and M-9B, were optical sights. If you couldn't see the ground and target you didn't have a sighting system at all.
US bombing using radar (H2X) was woeful, the results were often worse than those admitted by the British in the Butt Report. There are several reasons for this, beyond the scope of a concise reply.
Cheers
Steve