To pass ATPL theory, I'd say the maths is no worse than needed for a good grade at GCSE. There's no calculus and very little mechanics, just rote stuff really. To be a smart pilot who can instantly recalculate for anomalies, you still don't need calculus, but you need better than GCSE maths, and IMHO you owe your passengers more than you can swallow by rote and regurgitate simply as abc or d