I think in general:
- the comments are being used well
- moving things to chat rooms will be counter-productive
- the chat rooms are not conducive here (in phil.SE) to productive discussions
This is pointedly in general; I'm sure there are instances of comment exchanges that are not productive. But I don't think they are as numerous as you.
Many of the lengthy comment threads are necessary explanations of the ideas in a question or answer.
Also, whatever the intended use of chat rooms (to have a back and forth where people explain terms at length and question what one really means, nothing really of import to the original SE question or answer but for the benefit of the discussants), it just doesn't work out that way. People are hardly ever available at the same time (that's exactly the benefit of the newsgroup/QA call/response mode. I believe if you summarily move a comment thread/discussion to a chat room, it will kill the discussion (that may be the intent, but I don't think it should be so).
This is not at all to say that the chat rooms -shouldn't- be used for discussions, I just think as they are engineered now and with the current behavior of participants, it's just not feasible to hold a discussion between two people. Visits to the site and even moreso the chat rooms are so sporadic that using the chat room is almost identical in behavior to responding comment threads, just not associated with a particular question/answer. (my limited experience of the chat rooms here at SE are that they are used mostly for socializing or gossipy meta-talk about the questions and answer at the main site.)
In fact, I'd like to see discussions in the chat rooms. I just don't think it is realistic to expect people to start using them even if pushed there.
To end on a more positive note, I think encouraging visits to the chat rooms in general is a positive thing, but to make that kind of encouragement successful, it would be better to encourage visiting the entire site.