Maybe the league considers positional caps if they can get it through the NFLPA. Or a player can't count more than x% of the total teams cap. The NFLPA may go for that as the money still would get allocated just not to 1 player.
However, you're right at some point teams have to consider if their tier 2, 3 QB is really a must re-sign.
that's going to be a dog fight for the NFLPA within their own ranks. if they put a cap on position salaries, any type of cap, then the position players may fight and argue back. so the players union has to approve that. it may start with QB, then who is next? WR? DEs?
the owners don't care. there is a cap floor spend and cap max they have to manage against, and they don't give a darn who gets paid. the market will set the price and they have a range to stay within. they may not be interested at all in position caps, because it creates further complexity for them.
I think the cap works as it is. smart teams are able to put toghether a good team, play in championships and be lucky enough to winit. every year there is two teams in superbowl. 4 teams in league championship games, etc.
and the market is driven by supply and demand. there is one mahomes, one burrows, with Allen a close third, then there is 29 others.
some teams are smarter than others. (philly, Detroit). some aren't so smart (Cowboys).