Personally, I wouldn't mind if TPTB arranged for the Community user to periodically delete a few older comments at random. In fact, I could easily be persuaded this would be a good idea.
I've no doubt that in their capacity as moderators, our mod team would all agree that I post far too many comments on ELU (particularly, comments that aren't directly relevant to the post in question). I probably won't change my behaviour unless I'm specifically taken to task over this, but I certainly wouldn't expect to win the argument over whether I'm in the right or not.
In case anyone has trouble finding the relevant Help Page, in essence it says...
Only posts comments to...
1: Request clarification
2: Leave constructive criticism that may prompt someone to improve a post
3: Add relevant but minor or transient information to a post
(e.g. a link to a related question, or an alert to the author that the question has been updated).
Don't use comments to...
1: Suggest trivial corrections (instead, make or suggest an edit)
2: Resolve the OP's question (instead, post an actual answer)
3: Agree or disagree (instead, use up/downvotes)
4: Start or continue extended discussions (instead, use 'chat' or 'meta')
The bottom line is comments should be seen as ephemeral. If there's anything important that needs to be preserved, it should be in the relevant Question or Answer (or you should post a new Answer). But unless the mods start complaining about the excessive workload caused by non-observance of this principle, I see nothing wrong with the way things are currently handled.