In March, Tom Brady left New England as a free agent to replace Jameis Winston, once the first pick in the draft, as Tampa Bay's starting quarterback.

Three years ago, Patrick Mahomes replaced Alex Smith, once the first pick in the draft, as Kansas City's starter.

On Sunday, Brady and Mahomes will face each other in the Super Bowl, proof that freedom of quarterback movement can be fascinating and fruitful.

Vikings fans know this. Their best two Vikings teams of the past 44 years were led by older quarterbacks who previously starred for NFC rivals — Randall Cunningham and Brett Favre. And the Vikings' glory years occurred after they traded to get Fran Tarkenton back from the New York Giants.

This year, the most intriguing story lines of the young NFL offseason involve one blockbuster quarterback trade — the Rams and Lions exchanging starters — and a slew that could happen.

Carson Wentz and Deshaun Watson want to move. The Cowboys don't seem to know what to do with their franchise quarterback. The 49ers, Saints, Panthers, Washington, Bears, Colts, Patriots, Dolphins, Jets, Jaguars and Broncos are or may be looking for a new starter. ESPN reporter Adam Schefter has speculated that 18 or more teams could have new starting quarterbacks next season.

Brady, Mahomes, Cunningham and Favre are four good reasons why the NFL needs to alter the way it manages its salary cap.

The cap in itself is a good thing. It rewards intelligent management and prevents larger-market teams from dominating the sport.

But the penalties built into large contracts are counterproductive and prevent teams from making the kinds of moves that would make the league even more fair and fascinating.

The Eagles drafted Wentz with the second pick in the 2016 draft. He had one season in which he was an MVP candidate before getting hurt, the Eagles won the Super Bowl without him, he went into decline and now wants to play elsewhere.

If the Eagles trade him, they would suffer a cap hit of $34 million.

Why?

Why punish a team for wanting to trade or cut a player?

Wouldn't the NFL be a more interesting league if the Eagles could trade Wentz today, hand the job to Jalen Hurts and know that if Hurts doesn't work out they can simply try again, via the draft, free agency or trade, without suffering a financial penalty?

Remember, Favre had to leave Green Bay for the Jets, "retire" and then unretire to play for the Vikings. He shouldn't have had to jump through any hoops.

In this Super Bowl we'll see the culmination of two of the league's best stories — Brady leaving Bill Belichick and the Patriots to immediately elevate another franchise, and Mahomes making the case that he is the greatest young quarterback ever.

If quarterback movement was less onerous, the NFL next season could have seen Matt Ryan in Indianapolis, Aaron Rodgers in San Francisco, Watson in Chicago, Wentz in Minnesota, Kirk Cousins in Atlanta, or maybe the Vikings trying to finally draft their long-term franchise quarterback.

Instead, many teams wanting to change quarterbacks may have to wait until the cap hit on their quarterback is reduced in a year or two.

Who does this system benefit? Not players. Not the teams. Not the league.

It's possible that the Vikings might stick with Cousins even if they could trade him without being financially penalized, but they'd at least be looking at the market to see if they could do better. Given that his dead cap hit for 2021 is $41 million, his dead cap hit for 2022 is $10 million and he becomes a free agent after that season, the Vikings are most likely to wait at least a year before moving on from him.

Think of this in marketing terms, if marketing teams had to imbibe truth serum before crafting their ad campaigns: "Kirk Cousins: He's Our Guy. We Have No Choice."

Wouldn't it be better if all teams could change quarterbacks whenever they liked? That's what the Bucs and Chiefs did, and the result is one of the best quarterback matchups in Super Bowl history.

Jim Souhan's podcast can be heard at TalkNorth.com. On Twitter: @SouhanStrib. jsouhan@startribune.com