We all remember well, how Steve Jobs famously saved Apple by ruthlessly cut the product portfolio from tens of products to just four products. Using the famous four quadrant product grid he focused the offering on serving consumers, professionals, desktop and portables (mobile).
If you struggle to win a strategic advantage or even fear losing it, go back to task one and do more research to better understand the problem. Don't ask "What more can we do to win?" or "How can we prevent all of our projects to fail?". Instead, ask "What are the 1, 2, or 3 priorities we must focus on, and how can we ensure those go spectacularly?".
When you're confronted with a question like "Should we deliver this mediocre thing, or should we spend additional resources that we don't have to make it better?" the fight has already been lost. The thing you failed to do months ago was prioritizing aggressively enough. Either this thing matters, in which case you make it great. Or it doesn't and you don't even initiate it in the first place.
You need to establish a culture within your company and team that celebrates saying "No" and embrace a ruthless prioritization workflow that leads to more effective roadmaps.