The number are VERY possible to reach in a way that you reach a statistical parity, my numbers for 1712 posted earlier are my actual numbers with gear equipped and I use a spreadsheet to balance, so I am only a bit off (less that 20) on all the stats listed for 1700.
It really depends on the class you're talking about. Remember, Shield doesn't compete with Defense or Absorb through normal gearing means (re: everything except for augs) so, assuming you're stacking your mitigation and using high Shield enhs, you're going to have a functionally static amount of shield. You can't lower that shield to increase your absorb or defense, so, sometimes, the explicitly listed optimal ratio isn't really accessible without dropping your total stat budget (this is going to happen a lot with Guardians and Shadows). VG don't really have this problem because they want to stack the living hell out of their Shield.
Why would you never devote augments to shielding?
You can get all of the Shield rating you need by simply using high Shield enhancements (which you're probably using anyway to get to said high stat budgets). Since Shield only competes with Endurance (and Accuracy, but who cares about Acc on a tank) but Defense and Absorb directly compete with each other as well as Endurance, you should be auging for Defense and Absorb to reach the appropriate level of parity within your given stat budget.