The show is inconsistent with Barry's speed. One episode has him moving fast enough to have a one sided conversation with out Iris hearing or seeing him. He also catches things by reflex (falling coffee mug). But he's often caught by surprise. Most of the time, he has to actively enable his speed force based powers for him to move or focus at super speed. When he does, his eyes flash with Speed-Force lightning.
Quicksilver in most media is always at super speed, as I mentioned in the other answer He doesn't tap into a speed force, he has natural genetic quickness. In X-Men, he's significantly ADHD, and in MCU, he even sees a bullet shot from under him (but he can't react in time since he wasn't paying attention to it below him)
That said, there is multiple instances of Barry, Eobard, and Zoom catching bullets in mid air. Barry for example when Papa Snart shot him, he caught the bullet in his hand while pretending to have been shot. Zoom when The entire CCPD shot at him. Zoom also pretty much recreates the X-men Quick Silver scene when he kills half the CCPD on both Earth 1 and Earth 2, immediately snapping all their necks, so they all fall at the same time.
Barry doesn't do this because he is hampered by the Good Guy Idiot Ball, and as you mentioned, is plot dumb. That said, he swoops in and takes out a huge crowd of Meta humans from Earth-2 in the second to last episode, essentially like zoom did, just not fatally.
To provide a comparison, Barry Allen in The Flash has rescued buildings full of people while one building is on fire (S01E02), and later when another building collapses (S02E22). X-Men Apocalypse shows Quicksilver do the same to a mansion full of people while the mansion explodes. The only difference being the special effects budget used to show this happening. The end result was the same, a group of people single handedly saved by the speedsters, initiated by a split second reaction to building destruction events.