I don't even think it's possible to NOT have a useful effect with biotics aside from explosions, for example with Warp debuffing enemies and Reave draining them for extra damage reduction on yourself. No one in their right mind would spec or even use a character with a biotic power that wasn't for a purpose so your post doesn't really make a point.
Sure, Warp reduces armor and has Expose... and vanishes the moment i blow it up with another biotic power.
Reave i don't use, for i don't play characters with Reave (because their other powers are weak, boring or just not for me). Oh and i'm never quite sure just how Reave works in ME3: Does the damage reduction last only as long as the Reave is active on some enemy, or does it simply activate for the duration when Reave is used on a valid target, even if the target dies right away? Either way, i don't care for it, i can stick to cover to avoid getting shot. My characters are glass-cannons...
To me, Biotics are a method to do immense damage, any extra effects are just a bonus and temporary, not something i think about.
Applies to Tech powers as well, if i play a tech class, i pick one with freezing and burning effect and use cryo and fire explosions (usually the former, easier to set up and detonate) to deal maxium damage.
EDIT since i play mostly (99% of time) with PUGs, i sacrifice any utility for extra damage as that servers me far better than utility my random stupid team mates don't take advantage of.