I think it is more accurate than you are giving it credit for being.
Fargo rates players within an ecosystem, based on wins and losses of games. It does not care if they can pocket balls, play safe or kick, or anything else. The only data is "who won."
Then, it builds from there on "who did THEY beat? And who did they lose to... and who did THEY beat, and who did they lose to..." on and on.
Fargo builds a pyramid. There will always be a point at the top.
In a year that a top player dominated the tournament scene, like Reyes, Strickland, Varner or Segal, they would have rated in the 800s because they were beating everyone, and the "everyone" they were beating were beating everyone else... and so on.
IF there is a case that the ecosystem was not as strong (there was less international play, for example, creating less "connectedness") the tip of the pyramid might be a few points lower (790, not 800) but not much more than that.
HOWEVER... do I think that yesterday's 780 would compete with today's 780? No. Today's 780 has achieved that rating against a tougher set of opponents (inarguably a deeper field).