FC averages are considered a joke because conditions vary massively from region to region, to the point where they overly favour a certain style of cricketer.
For a while we had an epidemic of overly green, swing and seam friendly pitches in a few places, which saw the mediocre trundlers from those states end up with fantastic stats each season, that were not a fair reflection of their talent. Naturally any batsman who could score on those pitches was rated highly.
Similarly Jadeja's home state plays on pitches that are notoriously flat. But that then makes his bowling stats look fantastically good, which is fair. The guy is a gun bowler at domestic level if nothing else.
And then there are some dustbowls going around which leads to very one dimensional spinners ripping through sides.
Add to that the fact that we have so many teams, it's hard to gauge the quality of the competition sometimes. For instance, Pankaj Singh is now playing for Puducherry, and his games are still considered FC status like when he played for Rajasthan. But he is playing a much lower level of cricket, and this season has 31 wickets @ 7.
Cricket Records | Records | Ranji Trophy, 2018/19 - Puducherry | | Batting and bowling averages | ESPNcricinfo
So yea...Ranji FC stats are totally useless on face value. You really need to dig into them to understand the conditions/quality of opposition.