Working with only the rectangular outlines is both part of the purpose of all cutlist programs and also a shortcoming that would be extremely difficult and potentially useless to overcome.
The purpose of a cutlist is to let you know how much material you need to purchase, and most also have a layout feature that shows where you are supposed to cut each piece from the stock. But it is geared toward assessing the minimum requred raw stock, hence doesn’t take into account anything beyond bulk rectangular shape.
The shortcoming is that is cutlists don’t take into account the ways you could nest parts to get more out of the same boards. In your example, if two boards have cuts at the same angle, you may be able to fit them end-to-end against each other overlapping the points. Similarly, two curved pieces might be able to fit side-by-side across a board tighter than their bounding boxes allow.
But even more important, no cutlist program is able to account for the flaws and features of the stock. You can’t tell it where there is a knot or a check, or how the color and figure run in a board. In everything except un-figured sheetgoods or painted wood, those are aspects that affect how you will cut your parts in the real world . Unless you have the luxury of picking from a much larger stock to find ideally matched boards, you always have to allow extra in what you buy. The cutlist totals are just a starting point.