Robustness of user interface inversely proportional with investment into training users to use the software. So, design gets ROI as you scale (and not before). Or, in places where the software must “train” customers at a very low cost (like freemium saas products). Great design lowers CAC by boosting conversion rates due to difficult software.
“If you manage your top line (quality of your people, quality of your products, quality of your strategy), the bottom line will follow.”
-Mentor of Steve Jobs