No matter which chat service you use, any recipient could potentially upload the unencrypted data to a cloud backup service. If you don't trust the intended recipients with the data then you shouldn't share it with them in the first place.
This is a great - and often forgotten I think - point.
I guess my point is that in WhatsApp it is so easy to stumble into doing it, and that it sends it directly to the cloud.
For clarification: I'm certainly annoyed at Google for a number of reasons, but I don't think their security record is worse than everyone else's. Quite the contrary.
