First of all, if you have personal rating issues please sort between yourselves as fellow users in kind, and if it's with reviewers or moderators, please use Staff Contact to sort the matter. I'm just stating this beforehand. Now, to the matter:
The system have much altered since Hive 2. Well, the current administration cannot tamper with old reviews as that is like dishonoring the predecessors and they review with their time of standards.
There's a reason why I try to never rate resources unless specifically demanded by the author. The current rating system has been too much of an issue that there are plans when moving to XF2 to have an alternative system for users to express their opinions. A drop hint I recall it's a like system of sort.
And in the current system, actually everyone can review (mod/reviewer just tag them as reviews), and there's no such thing as mod review anymore except for approval processing (which should be separated from rating issues). It's just that since mod/reviewer reviews are auto tagged to the review list, they get visible, which makes them kind of annoying for some people. I think I can ask for review's ratings to get removed from review list, so any rating issues becomes a personal person per person issue, which at that point is all about personal taste.
In terms of singleplayer being more likely get 5/5 from regular users, it's something that we cannot tamper much with. Regular userd have their right to express how they rate. If this irritates much, please be patient until the new system is ready.
@omidh we have a team here, but the problem is we don't share timezones and have different availability times adding complexity to multiplayer testing. Please provide maps with 5/5 rating you mentioned. I would like to see the time of it's review.