When the D or ST scores, we technically use up our possession and must punt. The offense can't even take the field, so any "per game" metric like these punish an offense for possessing the ball 0 seconds and 0 yards. The opposing team gets two possessions with all those offensive minutes and offensive yards (and perhaps offensive scores) in that time.
(Not to mention the short field "problem" pointed out above).
So yards per game and offensive points per game is not really the best measure of offensive performance.
Here's a little stat I go by to tell how good we are overall: Wins/Losses (this year we're infinitely good).
If that's not good enough, Wins/Losses with a sprinkle of Wins/Losses of our opponents compared to others (IE Strength of Schedule/Strength of Record) who also return "infinity." We're still very good (#2?) in that metric.