It's true that Crosby has been better over the past six seasons with the Packers ranking 18th in the league in field goal percentage over that period. Still below average though.
I believe 18th. is an accurate representation of Crosby vs. the league. Considering the league average sits between 16th. and 17th., he's in the average range. What's the difference between 16th. and 18th.? A percentage point? One miss over 3 years? Then you get into distance distributions, stadiums, and a consideration of EP and KO performance.
Last season Crosby was 18th. ranked, 0.7% lower than the two guys ranked 15th., equating to 1 extra miss out of every 143 kicks, one extra miss every 4 or 5 years, with a higher percentage of his kicks from 40+ than those two 15th. ranked guys, 59.5% vs. 47.8% and 50.0%. That seems to be a fairly representative season for him.
In aluding to other posts, there's a reason why comparing Crosby's career record to that of kickers of more recent vintage is the distortion caused by the continued advancement in the state of the art since Crosby's rookie season.
https://www.pro-football-reference.com/years/NFL/kicking.htm
Prior to his rookie year, the highest league average for a season was 81.4%. The averages have continued on a steady uptrend in fits and starts. In 2007-2012, the league average low/high were 81.3%/84.5%. In 2013-2018 they were 84.0%/86.5%. The trend may be leveling off with the the peak coming in 2013; The last 5 years have been in a tight range of 84.0% - 84.7%.
In the last 6 years Crosby has been above the league average 3 times, below 3 times. His average for the period is 84.2%. His high low were 78.9%/89.2%. That's about as average as you can get. Again, one missed kick out of 33 in a season, which could be caused by any number of factors, is about 3 percentage points and multiple positions in a seaon's ranking.
With the exception of one outlier season on the very low side and one on the high side, you simply cannot convince me that Crosby has been other than in the range of a reliably average NFL kicker, sometimes a bit lower, sometimes a bit higher.
Looking backward, has he been overpaid? To repeat, yes. Looking backward, should Cobb and Matthews been cut before last season? Absolutely. 20/20 hindsight is a *****.
But where are we now? $3.1 mil in cap savings over a first year minimum guy like Ficken? That would be nice providing Ficken proves to be reliably average. If he's striping FGs and TBs in preseason then go for it. However, if he sh*ts the bed under the regular season bright lights, which is not uncommon with unproven kickers, I think you will have been happy to have overpaid Crosby $1.0 - $1.5 mil over what you should pay for reliably average.
The best argument I can make for taking the risk of replacing Crosby at this time with an unproven Ficken or some other to-be-named player is that this is not a championship caliber roster in the first year of a what we hope to be a relatively quick rebuild. Running through a few failed guys in trying to find a winner won't deny the ultimate prize.