I trust more TSMC process numbers (for large changes, not the 4nm bulls*t) more than battery life published by a PR/marketing team for my buying decisions. They are much harder to fake. And sure, performance/watt is what matters generally, which is again hard to compare between brands and marketing teams.

Even then, I would say you care about battery life and performance/Watt, and think process node a better proxy for them than what manufacturers and reviews say about them.