Well they could just remain as normal comments then rather than labelling and separating them, and requiring moderators to read them.
If they are just normal comments then you lose all control. Either the jerks can post anything they want including comments like "This mod sux and the creater should die becuz he maed her eyes green and i wnat them blue." or the modder can remove legitimate complaints like "If you install and use this mod for a day or so there is no way to remove the mod and continue using that save. Make sure to create a backup before testing this mod."
If the complaints/criticisms have to be labelled and approved, then the modder can clean his own threads of stupid comments, but the legitimate complaints/criticisms are still protected.
And the mini-moderators wouldn't have much to do. All they'd do is confirm if the post has legitimate content instead of being a pure flame and either approve or reject it. If rejected the user would have the chance to re-phrase their complaint. Most of it would be automated, and since the mini-moderators wouldn't have any significant power you could have quite a lot of them.
If the user feels the mini-moderator was too strict, they could re-submit and a different mini-moderator would get the chance to approve. To keep the real mods from being too busy, you could limit complaints about the mini-moderators to have a threshold, so that more than 20 people have to complain about a mini-moderator before a Full moderator is notified. Or 50, or 100.