I think you are missing the point and overrating our back line. You seem to infer our back line can be solved by one player as a final solution and its all ticked off and appear to be anchored by a back line currently operating through Chaplin's involvement as adequate in terms of set-up. This is far from our premiership requirements IMO. I see the current setup as purely stop gap and ineffective against better forward structures. I see Collins as simply stage one in a two part recruitment strategy. The bigger forwards you speak of will not be addressed till later with another recruit or recruits which boost our KPF set ups as well. In the meantime one can play Astbury and Chaplin in the side as well.
There also seems to be a short term focus on next year which is unrealistic as we do not have the team to be in contention yet. We have not picked up our doozies yet so why fuss over the realities in 2016? Having said that physically I think Collins is more mature than Lever despite his age and could easily make an immediate impact not to mention releasing Rance into other roles. Eg ATM our only FB option is Rance why reduces our flexibility.
194 cm is a superior height than 197cm and above as a KPP generally however the fact Collins has good agility makes him relevant on the smaller types and therefore effective. The pedigree of the player and his movement is critical IMO
I don't disagree that Chaplain has a lot of holes in his game. But I also see that he brings some traits that help others in our backline. Could we do better and should we do better - I think we should. I just don't see a rookie, even one as physically gifted as Collins is as being able to hold down, week-in-week-out a first or even second key forward. Your looking at a McCarty or Patton from GWS. A Dixon for Port. A Jenkins from Adelaide. A roughead or Gunston from Hawthorn. These types (and I could go on).
Historically speaking, it requires more than a few years in the system to be a capable key defender. Rance and to a lesser extent Hurley are cases on point. McKenzie and Talia are others. All of which showed ability as Collins does, but they needed time to go into that role.
Lever has been the example thrown about, but again I say he's a third or fourth tall. He shown some capability in his draft year/ before (due to ACL injury) to push up the ground into the midfield.
We have Astbury (we tend to forget how good he was prior to the game in 2014 v Melbourne) and Elton who has better physical attributes than Collins does.
Again, Im not saying stay well away from this kid because with time I think he will be very very good. I just don't think its realistic to expect him to be good enough to hold down a key defender role for 23 games plus a year i a side that has top 4 ambitions from here on out.