[hammock]

>Surely an UI with controls specific to the task at hand is much better than having the user guess what the bot responds to and what it can do?

The challenge of syntax discoverability can be mitigated in a text interface with smart autocomplete to guide people towards what they can say. It becomes harder with voice. Also one messaging app, Telegram, allows chatbots to present customized keyboards that change based on the context of the conversation, e.g. thumbs up/down or star rating system.