"You have to subscribe to something batteries-included, like Meteor, or otherwise implement the solutions yourself from bits and pieces."

...yes; that is, in fact, the conceptual dichotomy in solutions to essentially-complex problems. Either someone else solves them for you, or you have to solve them yourself.

I mean, yes, there is a part of the solution-space in-between these two extremes — a point where there's a batteries-included thing that someone else built but then gives away for free, perhaps as an open-source project you just have to run on your own infra. So it's mostly solved for you, and then you just do a little bit to "get the solution running" for your use-case. That point in solution-space is conspicuously absent for web data sync.

But, in domains with essential complexity, that middle-ground part of the solution-space is usually conspicuously absent. Because it takes continuous dedicated effort (i.e. labor; capital expenditure) to solve the complex problem in a cleanly-abstracted way. And it's very rare that anyone's going to go to the effort, unless they expect a return on their labor investment (by e.g. keeping the solution proprietary, and building a SaaS business around it.)