I appreciate the package author putting this together but with Botkit as well... I don't know. That's frustrating dealing with multiple APIs. Botkit is adding support for Facebook too.
Would be nice to have one. https://github.com/howdyai/botkit
However, I do think messenger-bot serves a slightly different purpose than Botkit might. messenger-bot is mostly just a library over the Messenger platform, with some events and convenience functions. Botkit is a bit higher level though, since it includes extras like conversation sessions, pattern matching on messages, etc.
I think both libraries have their upsides and downsides, depending on the use case. Up to the author to choose what's best for them!