I will post full stats on this later but for now just trust me. Good key forwards are the absolute hardest players to get, and they should have the highest valuation on your list. They are either first round picks or they are shenanigans like father/son and prelisted.
By contrast, key defenders are some of the easiest players to get at a good level. Rookie draft picks, mature age draftees and shitty ND picks from 50+ routinely become good AFL key defenders. It happens incredibly rarely with key forwards.
The lowest value players on the list are small defenders like Nick Smith. Pigeonholed small forwards also have low value (ones who can be midfielders are significantly more valuable).
What does this mean for us?
1) Kurt Tippett despite being overpaid and not perfect absolutely should not be traded. We can't replace him as a key forward (as a ruck we easily can)
2) Guys like McLaren etc will never, ever become gun key forwards. Not happening. They should be developed as defenders.
3) Trading big currency for a key defender is not ideal. Some of them are high draft picks but an equal number can be found in the 3rd round, 4th round or rookie draft if you are good enough.