AC is much more balanced in this edition. You gain one armor bonus, one shield bonus, 1 feat bonus etc... and only 1 enhancement bonus to AC.
You will find that the +2 shield bonus to you AC is just as valuable at high levels as it is at low levels. We are no longer in the zone of 3e where the monsters you are fighting have some random value from 5%-95% chance to hit you. The game is balanced better now so that the extra bonus of having a shield usually makes the difference between 50% and 40% or the like.