There is little doubt that clubs could (and previously have) commanded more per key position back when there were less advertising spots on the jerseys.
The battle you'll have however is for those clubs who have good commercial teams (ie. Rabbitohs, Broncos, Storm) they would push back on any reduction of sponsor spots because they have been able to extract good dollars for every one of them and won't be prepared to just let it go, whilst for the clubs that struggle to sell (ie. Dragons, Manly, Bulldogs, Sharks) they'll push back as it makes their job harder.
Most clubs set themselves a target of $2m+ in revenue from kit sponsorship these days. For some clubs like Brisbane or Souths, they get more than half of this in just the front of jersey sponsor, whilst others, like when the Bulldogs first signed Laundy, are more around the $600K mark (I'm sure the renewal is at a higher rate, but I doubt it's at or above $1m), meaning they need the likes of sternum, lower back, etc to get close to their targets.
Not saying it's right, but this is the battle. The fact AFL has strict standards both on what can be sold, but as well size & experience of commercial teams, and gives grants / fund proportionally to help lift minimum standards pays off nicely for them. We can thank John Grant for throwing out that concept to try and keep his spot on the Commission.