It might be worth trying to convince the decision makers that a lot of thought went into Discourse’s design. It’s intended to promote the idea of conversations, as opposed to a one-off comment system where each comment is expected to stand on its own. That’s why things like reverse post order, or promoting the most popular comment to the top of the thread were not implemented.
I agree that the UI could be simplified. You might get some inspiration from Sam's Simple Theme. I think it only deals with the topic list page, but it gives some ideas about what can be accomplished with CSS.