It’s not a single rule per order, it’s a single rule per line item on the order.
This takes us back to what was mentioned in Price books rule with different discounts per product type, where (unless you wanted the multiple rules to all apply after each other) there would have to be some way to tell Breww to disregard a suitable rule for one later down the tree, even though rules which you have placed as a higher priority fit the line item first.
I do agree with you that it is already complicated to the point where it can be difficult to use, which is why we are sceptical to add further to it. Of course, if there are lots of customers who cannot do their discounting via Breww because of this, then we will certainly look into it, but this is the first we’ve heard of this specific problem.