But they could be, my suggestions.
Give them melee powers, on my Elec/Elec Sentinel I am in melee range all the time anyway, why not have a punch or 2.
Shields 'Grant Cover' power, either make it inherent or give it as a toggle. This would give more of a need for them in teams, maybe even give it a lesser taunt effect.
"You are able to use your shield to defend nearby allies. Any teammates who remain nearby gain a bonus to their defense. (NOTE: The defense bonus from this power is only applied to nearby team mates, but not yourself.) Additionally, while this power is active, the user and his team mates will gain some resistance to defense and recharge rate debuffs."
Or something to that effect.