"Both GitHub and outside researchers have observed positive impact in controlled experiments and field studies where Copilot has conferred:

55% faster task completion using predictive text

Quality improvements across 8 dimensions (e.g. readability, error-free, maintainability)

50% faster time-to-merge"

how is time-to-merge a vibe?

The subject is productivity. Time to merge is as useful metric as Lines of Code to determine productivity. I can merge 100s of changes but if they are low quality or incur bugs, then it's not really more productive.