By my count, Grupe's 80% made field goals is 24th in the league among kickers with 25 kicks or more. I'm pretty sure the more difficult situations you mentioned for Grupe are also factored into the other kickers percentages as well. Will Lutz is ranked 13th with 88.2%.
Grupe made a lot of field goals because we kicked a lot of field goals because our offense is bad, especially in the red zone. He also missed a lot of FGs. Like when a linebacker or a safety on a bad defense has a ton of tackles because the team can't stop the run before it gets to them. Or a QB with 350 yards passing in a blowout loss because they are trying to play catchup all game.
Also, referring to people with realistic criticism as "haters" always sounds so childish. When it comes to overall FG percentage, we cut a long time incumbent that was slightly above average for a new kicker that is ranked near the bottom. Criticism in that regard is definitely valid.