Be careful about vanity metrics. If engagement is low then likely a large number of those users have already deleted the app and moved on. Focus on growing Monthly Active Users.

My suggestion is to find a vertical to focus on as there seem to already be many messaging apps out there. Ie. don't attack the big players straight on, find some niche that they aren't addressing.

E.g. physicians have special needs, so you could offer messaging for them & provide patient privacy.