bard has a very strong shield + damagereflektion and a near lackless rotation for defencebuffing while engi has a gap in shielding where he can use his other rescueskills
engi has the ultimative saveskill and teleports just away somewhere into invis while bard gets only 90% damageabsorb
Seems outdated to me.
Both supports offer the same amount of defense, with engineer having the advantage to reset Power Field.
Both bard's acoustic barrier and engineer's Iron Curtain do the same thing.
In short, the classes are very similar and have minor differences in the role they play and gameplay.