I'm on the verge of getting my assassin to 50 and wanted to start reading up on this stuff.
Anywho, I take it when you say absorbtion at 60% that includes the base generator 20% as well, right? And I'm assuming you're applying the bases to defense and shielding as well? Just wanted to check. Also, are these stats typically achieved through augmenting or no? If they are which augments should be prioritized?
Of course it would not even be possible to reach said percentages with the ratings alone.
But anyway you are missing some important things.
Your absorption without any absorption rating gear, is not just 20%. It is 24% due to additional 4% from skillpoints spent on Hollow.
Likewise your defense chance without any defense rating gear is 16% (10% base + 6% from various skillpoints spent in the skill tree), so even at 30% defense chance you have 14% defense chance gained from defense rating.
As for shield chance, note that any percentages given with Dark Ward activated should also include the bonus from wearing gear with set bonus. (speaking of which, assassin tanks should ALWAYS wear gear with set bonus)
As for the other things, augmenting should be done for defense rating and/or absorption rating, depending how much of each you have