Should top finishing teams be restricted during Free Agency and Trade periods?

Essentially the idea of a salary cap is to ensure that the gap between the top teams and bottom teams is relatively small as each club only has the ability to pay players a certain amount and therefore have to relinquish players when their overall talent pool is too great. 

But does this really happen?

Sydney won the 2012 AFL Premiership over Hawthorn. However, instead of losing players of particular note or being limited in their ability to obtain good players during the off-season, they were able to acquire Kurt Tippett from Adelaide at quite a high salary. Further to this the following year to rub salt in the wounds of all the clubs down the bottom of the ladder they acquired Lance "Buddy" Franklin in the largest contract in football history. The only player they parted with of note was ruckman Shane Mumford, who at the time was being beaten by fellow Swan Mike Pyke.

What is really being eluded to in these actions is the fact that Free Agency and Trades do not favour the weak teams at all. Instead it is an opportunity for players seeking more on-field success to move to better clubs. So far no club has really propelled themselves back into the top frame of the competition using free agency. Instead most clubs have struggled because the free agents have cost them a considerable amount of cap space and as a result they have lost existing players instead.

Overall, it is believed the system needs a complete overhaul that favours player development by clubs and ensures the big clubs don't control the market.