Comment by aboodman

Well that "make a mutation client-side" phrase is doing a lot of work.

Make a mutation to what?

The classic server rendered web-app doesn't have any data to make a mutation to. You could try to patch the UI but that would be a huge pita and not really a scalable (in effort) solution.

If you have an SPA, you still don't really have data on the client-side. You have a bunch of cached query responses. You can update those, but (a) it will be a pita to do correctly, (b) you'll have to do it to every possibly affected query, and (c) you have to remember to undo it at the right time (way more subtle than it appears - think it through!).

A sync engine creates the client-side normalized datastore that allows you to "do a mutation client side". In fact, you're kind of right that once you have a sync engine, just doing a mutation is really easy. The real challenge is all the infra required to enable you to do so.