If we were cast away to some prison like existence where we could only have access to one metric - we'd choose Time to Interactive metric (TTI) every time. TTI is so impactful, we've even built a tool to help yo guage the impact it has on your site.
TTI is similar to the DOM Content Loaded metric - but historically is more dependable. At Edgemesh we find TTI to be consistently reliable proxy to core KPIs such as Bounce rate. Below is an example report showing the relationship between TTI and Bounce Rate based on 1 month of real user interactions.