I understand the idea of wanting comparative balance by having the luxury tax, But...
Part of appeal for the fans is to follow young players in your organization. Someone such as Xander and Betts.
I suggest MLB in next CB, place a hard cap on AAV for a 'home grown talent" at say $25M. Thus if Betts receives a 10 year, $300M contract, Sox would only count $25M for the purpose of luxury tax. Each team should be 'rewarded' for developing players in their farm system.
You can tie in the hard cap with let's say a percentage of top 5 multiple years contracts in the league. But once the hard cap is established for a player, that amount does not move in subsequent years when the top 5 pay in the league would steadily move up.
For the definition of 'home grown' talent, you can tie it to Rookie of Year qualifiers. Suppose Beni was drafted by the Yankees. But he will qualify for the Rookie of the Year balloting as a Red Sox, so he's eligible for hard cap only as a Sox and not the Yankees.
Ok, March Madness starts in couple of hours.