That's just as it should be.AS引导表语从句可以在表语从句中充当成分吗

可以的,as属于代词,在引导定语从句和名词性从句时,可以充当成分,但是引导状语从句时不充当成分,但有一定的意思。如： As is known to all, the earth looks like a ball。 As the time went on ,we made much progress。