In my opinion there has been definite development and improvement in our D overall. It's still not up to the standard of even the top 8 sides, however we are at least turning up to the confrontation now, where as not that long ago teams were pouring through our middle and commentators were calling our forwards 'soft'. Any time a team came within 30 metres of our line they would score. We could never defend a well placed high ball in the past (not 100% convinced we can now either).
Sounds like an obvious comment but, attack and defence go hand in hand. If we are constantly on the back foot and are losing the wrestle at the ruck (allowing quick ptb's) then we start to tire, the other team gets momentum and starts rolling through us. With this comes no space for our halves to attack and our players become too worn out to break the line when they do get the ball. Then comes dumb decisions, further fatigue and poor ball control, turnovers, penalties etc etc.
Those saying they don't care about defence are oversimplifying the game, and those massaging the stats to suit their arguments can perhaps show me stats on how many teams have made the top 4 in the last 15 years with negative F/A.