The roosters problems against top sides comes down to a couple of things.
They have no long kicking game at all, Keary and Walker can barely kick the ball 40m so if any team keeps them in their half they struggle to get out.
This also combines with a lack of metres from their backs compared to Penrith/Melbourne which means they can struggle if the opposition doesn't give them field position through errors or penalties.
Essentially they are good enough to score a ton of points if you give them enough opportunities but if you defend well, keep the errors to a minimum they really struggle in a grind.
I would personally enjoy playing them in the finals at Allianz because the refs will stop blowing penalities and we are generally a high completion team, the rooster's kryptonite.