Looking at package diffs is super important because of the rise of "protestware". For example, a maintainer of the event-source-polyfill package recently added code which redirects website visitors located in Eastern European timezones to a change.org petition page. This means that real users are being navigated to this random URL in production.
See the attack code here: https://socket.dev/npm/package/event-source-polyfill/diff/1....
It’s very unlikely that users of event-source-polyfill are aware that this hidden behavior has been added to the package. And yet, the package remains available on npm many months after it was initially published. We think that supply chain security tools like Socket have an important role to play in warning npm users when unwanted ‘gray area’ code is added to packages they use.
(Note: I helped write that. We're building a similar service to the r2c one.)
You're right that patching is hard because of opaque package diffs. I've seen some tools coming out like Socket.dev which show a diff between versions. https://socket.dev/npm/package/react/versions
But, that said, this is still a hard problem to solve and it's happened before that malware[0][1] has been silently shipped because of how opaque packages are.
0: https://web.archive.org/web/20201221173112/https://github.co...
1: https://www.coindesk.com/markets/2018/11/27/fake-developer-s...