It is not about being offline. It is more about running queries locally which makes them fast enough that you do not even need a loading spinner [1].
Imagine your whatsapp client would have to do a http request on each UI interaction.
I feel like the primary challenge of the field of software development is actually to guard simplicity. Local-first becoming a standard is not unlike SPA becoming the standard: it hurts simplicity and digs the hole we are in deeper still.
To help with this, I think any new technology proposed should advertise when it should NOT be used. In this case, I think, this disclaimer should probably say: "most of the time, for most applications, this should not be used".