I think you are misinterpreting why it moves to the top at first. It happens with movies on IMDb too.

The thing is that the players that are really into a certain game them/format, will be the ones who actively seek it out at first. And they will be more disposed to give it a high rating, because it fits with their preferences. Just like the first people to see a movie will, on average, be the ones with an affinity for that type of movie.

So the initial ratings will not reflect the average of the "general public". But the average of "people who would most likely like this game". That goes double for a game that requires translations at first. If there is a limitation on a availability the ratings will be dominated by the ones most eager to play it and most predisposed to liking it. See Dead of Winter. Currently #19 on BGG. It will drop. That the scarcity was cut along language edition lines and that BGG is English dominant is not as specifically important as you portray it.

As the game flies up the chart, it will then be picked up/sought out by people that want to see what the fuss is about, but are not necessarily into that kind of game. And the ratings starts being dragged back.

But yeah - of course it does not really say that #8 is better than #9 - especially if they are wildly different games.

When it comes to Caverna and Agricola you could glean some more pertinent information though, if you had access to the votes from people who had played both.

I think there is a misunderstanding about what best means in this context, though. It is merely a representation of the value of the entertainment the game provides. And on that aspect you can compare Agricola and Chess.

As far as who it represents - that would be the part of the BGG user base that rates games. The chart is a perfect representation of their evaluations.