But the infrastructure behind sounds complicated and fragile.

No, its complicated and scales to servicing every customer in the world. Thats not the same thing.

Doesnt mean the complaints about self-hosted arent valid, but "literally has to scale to the most insane volumes of data" and "is not good software" are two different things.

We're building a cloud service at the end of the day - its a lot easier to optimize a multi-tenant install than it is a single-tenant install, and that complexity shows up in the self-hosted repo. Can't really avoid it.