Coutinho to me is the type of player you add to a team thats already put together, he is the final touch that so many teams are missing. The final point you made is why we need reinforcements in the middle of the park and upfront. Better finishers will lead to better attempts which could mean more goals and corners. Better midfielders will anticipate where the ball is going, win more second balls and stop more counters in their tracks. Its no secret that our finishing is horrendous and our entire midfield is powder puff.
Once you have everything else figured out like Moyes has at West Ham or Wolves have, then you can start adding players like Phil and Emi2 who can open teams and create more chances. We're the complete opposite, everything is still up for discussion while we've two creative powerhouses stepping on each other's toes.