Actually, having 10% common functionality easily available for unsophisticated users, and the rest hidden but fast to access, is good UI.

Sure, discoverability is good to have, but it is not a failure that you need to be told about it as long as it only contains features useful to power users.

Requiring experts to undergo some training to make the most out of their devices is acceptable UI if the final interactions are optimized for their use; double so if it doesn't interfere with usage by untrained users.