Syndra is not good right now but not that trash like you think either.
Her R isn't a tool to just finish off someone, it offers more. It provides her a load of balls that she can E to find massive stuns in a fight.
I have seen a lot of Syndra players holding on R and still have it after a fight because they just use it for kills while they could have changed the entire fight.
People instead just use Q and E missing the stun on 1 guy most of the times.
I played Syndra a little ago and i think she can lane just fine and still bully some mid laners.
Of course she has seen better days but she can still perform well in the right match up and/or right hands.
Her damage is gated by her passive and people seem to not understand that.
And btw she can still blow a squiscy from 100% to 20% hp with just Q and E late game.