Without getting into a long debate rehashing the other 150 threads about ac, there is a simple balancing act that can help.
Shields in D&D are weak. DDO is not at fault for simply porting over the rules, but shields stink.
Any other game, a 4 -5 foot tall hunk of metal your hiding behind would do more than add 4 ac. Shields in history were used because they were useful and could stop a lot of incoming attacks.
Shields in D&D do not give enough ac to matter really compared to just doing more damage. Also, parrying is an option in some games that isnt in D&D. While tempest shield bonus is a similar idea (deflecting attackings with a second weapon) it really should be an option for all two weapon fighters not just rangers.
So the easy fix is to not only reduce all the stacking dodge bonuses that are driving ac up too high compared to others (icy should never have been added to the game), shields should give a +2 ac over what they are now.
So light shields +2 or +3, heavy +4, and tower +6. Blocking witha shield should be more than +2 ac, a full defence should be +4 more at least.
And blocking while two weapon fighting should give a better blocking bonus.
This would correct some of the imbalance that currently exists between the naked ranger/monks not only having twice the damage of a sword and board type, but that they also have better ac.