+1. Saying that Aegislash shouldn't be banned because there are ways to counter it doesn't make sense. There are ways to counter Genesect, Landorus-I, Blaziken, etc, but that doesn't mean they should be allowed. Also, Aegislash is a lot harder to counter than these Pokemon. Aegislash can be used with at least 5 different natures (Adamant, Rash, Quiet, Sassy, Brave), has King's Shield, and a ton of resistances and immunities.
These factors alone are not necessarily enough to decide whether Aegislash is broken or not. It is the combination of all these things that make Aegislash broken.