The thing to keep in mind about minor leagues is the players down there don’t make the same as they would in the major. They get what’s called 2-way contracts, an NHL player might get 4 million a year in the league, but if he’s sent down to the AHL farm he’ll make dramatically less than that (probably not more than 100K). And there’s nothing saying teams have to have these other players or a minimum number (might be a maximum), if they don’t want to have anybody developing in the minors they don’t have to. Meanwhile remember they already do carry extra players for the practice squad. And if your QB is in the minors he probably isn’t your new franchise QB, you’re hoping he is, but if you were certain of it he’d at worst be on your bench.
I think the rarity of games has more to do with unwillingness to develop players than free agency. With a 16 games schedule and the #1 seed usually going to teams with 3 or fewer losses you just don’t have the freedom to let a guy lose games for you while he gets better. You’ve always got the opportunity to keep players with contract extensions and the franchise tag.
There’s always going to be rules tweaks. As players get bigger, stronger and faster the old ways don’t work as well anymore, and smart coaches figure out ways to circumnavigate the intent of rules, and sometimes you find out that you wrote a bad rule. There’s always something broken, the problem is actually fixing it vs making it worse.