I feel like you're conflating a few different things here.

Small pages and interactions are good, sure, but I don't really see a tension between this and local first. My homepage is static HTML (minus google analytics) and it works offline.

The multi-mb JS bundle is also a red herring. The only multi-mb JS bundle I ever worked with did not work offline at all. Feel this is orthogonal.

Also connectivity for people is usually something that changes with time. You have it in the farmhouse, but not out in the field. You have it at the office, but not on the road. So downloading stuff when you have connectivity and still being able to read/write what you don't is the real aim of the game here.