This particular objection doesn't worry me, because all the really effective 'engines' I know about, that provide an environment to be built upon by others, are originated by and run by a single visionary person.
From my perspective, this is an asset rather than a bug, provided the person is committed to his project. It's a guiding force that stops it being a vague laundry list of feature requests.
But the worry here is that if the main developer of DragonRuby quits, it's dead in the water. Sure, you can use the old version and it'll probably still work, but there won't be any improvements, whereas other engines are constantly improving.