A cart-level code seems to be applied after our SKU-level discounts. Is that expected?

Yes, and the ordering is controllable and should only differentiate the result if one of the discounts is a fixed value outcome, as percentage discounts have a commutative property. Rules are evaluated in ascending sort order, so a lower sort order runs first. A rule marked apply last is evaluated after all other rules, which lets it apply on top of already discounted prices. Separately from ordering, a cart discount applies flat across the whole order and is not tied to the products that other rules discounted, whereas an item discount attaches to specific products. If you need the amount to interact with particular products, use an item discount rather than a cart discount. Note that the cart discount will always result in a distributed discount in relation to the product cost on the order row.