It's disingenuous to comare the "results" of salary cap by including the 10 years prior to the salary cap, the 10 years in fact that are why the NFL wanted a salary cap in the first place. It artificially weighs the data with completely contrary evidence. If you want to take the 10 years prior to the cap, the era of capless free agency, then you should just do a straight NFL to NFL comparison. The NFL pretty neatly devides into 3 eras: no free agency, free agency without cap, and free agency with cap. When you compare those eras with each other you'll see the middle era had the least competitive balance, even with the Steelers totally skewing the first era's data.
Yes recent sporting history, throw Nascar out because it's a very different kind of team sport and it's nearly impossible to compare to the others in any way, especially because there are different layers of teams, each driver has a team behind him, but there's usually a primary sponsor (like DEI) that forms a team behind the team which makes the picture incredibly cloudy, how many of those different drivers had the same shell team behind them, did any repeats switch teams? Too ugly to contemplate.
So in the other four notice that the NFL has more different teams winning than the other three, also dig into the finances and you'll find that the NFL is the only one of the four showing increases in attendance, TV ratings and overall revenue. Recent sporting history clearly shows that a hard cap is good for competitive balance and high competitive balance is good the sport's revenue.
Initially, I thought you were taking a devil's advocate position. But, obviously, not.
Bettman was the BRAINCHILD behind the NBA's HARDCAP agreement in 1983!
Since you want to compare apples to apples, let's see what the difference between the "1984 to PRESENT DAY HARDCAP" NBA reality is vs. the '64 to '84 timeframe, shall we?
From '64 to '84 there were 9 different teams that won the NBA championship.
From '84 to present there have been 6.
The HARDCAP sure brought significant improvement, didn't it?
How 'bout them apples (to apples)?
In 1994 the NFL hardcap took effect. Since that time (the 1995 Superbowl) there have been 8 different teams win. (8/11 73% variance)
In December 1975 the "Rozelle Rule", for compensated (read 'penalized') free agency, was struck down. The NFL predicted that all the good players would go to warm climate teams, or big market venues.
From the 1977 Superbowl to 1984, there were 6 different teams that won.
(6/8 75% variance)
In 1968 John Mackey won a landmark free agency case against the NFL. (But, in 1977 the player's union effectively reinstated the pre-1968 status quo with the NFL through the Collective Bargaining Agreement!)
In the years of 1969 to 1976 there were 6 different teams that won.
(6/8 75% variance)
Prior to 1969 the Packers won both Super Bowls.
Tell me again how the percentages have been increased by hardcap salary restrictions!!!!