In this case, even if you remove the ad-hominem attack (a bunch of randoms), a valid point remains: implementing crypto is already notoriously difficult, let alone designing cryptographic protocols.
In our case, we needed something that is both secure and competitive in comparison to mass market solutions in terms of speed, working on weak connections and usability.
Disclaimer: I work for Telegram.
Usability, however, is a different beast. You must compromise security to make a chat application appeal to "regular" users. Still, this is a trade-off that can be clearly communicated to the user and to developers, and does not require a custom crypto protocol. You can achieve the same effects with using existing and tested libraries.
Edit: Disclaimer: I am the developer of the yaxim Android XMPP client and the operator of the public yax.im XMPP server (both available at http://yax.im).
Now that google is killing talk in favour of proprietary hangouts, I predict it'll be a while before I'm a serious xmpp user again.
Sadly it's very hard to push process changes when one are in the minority in a group... Thanks for the reminder though, it does look like it full-fills most of my needs (and fixes annoyances I've encountered with other android clients).
Knowing this, I hope you can appreciate why the burden of proof on your unproven team and approach is fairly high.