For use case where cart quantity-based discounts apply, but only if a coupon is not being used. I've added a condition to the quantity-based discounts so that they only apply if the condition (see patch) evaluates as TRUE (i.e. order has coupon line item, negated).
This condition is closely based on a similar condition in commerce_shipping.
The 'any' option works but I haven't tested the option for a specific coupon code.