Besides, you are forgetting that shields are massively strong. I mean really, really, really
strong. Remember that ha'taks have the weakest shields of any vessel in Sgverse, and yet we've seen the shield of Apophis ha'tak take a 1 gigaton nuclear explosion in point blank and nothing happened to it besides that it shaked a little bit. If such a weak shield can resist a 1 gigaton explosion, then there is no reason to assume that mid to high gigaton nuclear explosions will take out the much stronger shields of Anubis' ha'taks, of Asgard motherships and Ori warships. The way to bring down these shields is not by brute force, because only probably a supernova or hypernova has the capacity to bring down those shields by this method, but rather to use specific beams composed of specific energy particles that make the shield oscilate, and concentrate all that power in a single spot until it collapses. Shields, even the weakest ones, are simply to effective at deflecting energy per square inch/foot of surface to be brought down.