If you don't raise int or dex as you increase level, you need to wear heavy armor if you don't want your AC to turn you into a beach ball at a Beach Boys concert. It is a simple fact in 4E - you either need heavy armor, increasing int/dex or a class feature to avoid seeing AC get ridiculously bad.
However, being a beach ball isn't necessarily a bad thing *if* the beach ball can survive being abused.
Assuming the shaman stands behind the front lines and sends his spirit into melee, these are a few fun facts:
Imagine a melee fighter that:
1.) Ignores bursts and blasts.
2.) Reduces all damage to 0 if it is less than 10 + 1/2 level. If it is equal to or more than that amount, the amage is reduced to 5+1/2 level insteadand the creature disappears until the start of its next turn, at which time it loses a minor action and can - as a free action - teleport across the battle field.
3.) Ignores stunning, dazing, being knocked prone, etc...
Pretty awesome, right? Sure, that disappearing thing can backfire and open a hole for enemies to pass through, but if you have another defender in the group, that situation can be mitigated.
That is what the spirit brings to the table as a melee force. In addition to that, you get to pile on some healing and a little controller ability. Nice, huh?
And, that melee force gets an old school cohort in the form of a shaman that can run around opening doors, providing flanking to help finish off nearly dead enemies, etc...
The original point of this thread was that the shaman's defense was too low... so what? So what if he gets hit too much. A well played shaman should probably see more attacks aimed at his spirit than at his person. If that is true, so what if the attacks hit all of the time? You can ignore the secondary effects of the hits, and the damage you lose is - at worst - reduced to 5 + 1/2 level each round.
Heck, I might think it nice to pick up stealth as a skill for a shaman just to help him hide in the back during combat...