At Barcelona, playing to the system is as important as breathing is to life. Malcom has shown that he has the potential to adapt well into the system here, which is exactly what Coutinho has failed to do in a year.
When Malcom is on the pitch, you can clearly see his attempts to link up creatively with Messi, Suarez, and Alba. And more often than not, he succeeds. He makes perfectly timed runs into the box and has even shown that his decision making is not hasty.
Coutinho has shown skill outside the area, but he has rarely if ever, posed a threat to the goal. When a coach plays you in the front 3, you are expected to cause some threat to the goalkeeper, and this is where Malcom trumps Coutinho.
Talk about finishing, and there is no doubt as to who has shown more promise. The variety of finishes that Malcom has displayed in just the 4–5 games he had played is outrageous and the El Clasico goal is the testament.
Coutinho too can provide top-notch finishes, but only when he is confident in himself. Right now, he finds all eyes on him, and all fingers pointing towards him; he is in his worst form ever.
Last but not least, Malcom provides pace, which Coutinho definitely does not. Coutinho tends to slow down the tempo(which is nothing wrong) but loses the ball subsequently. The Pace on one wing has now become a necessity, as it causes chaos in the ordered play of Barca, and adds another dimension to our play.
The game against Espanyol is the best example. They struggled in the first half, the team was weary and attacks were lazy. Cometh the second half, Malcom comes on, Coutinho drops to midfield and Voila! Malcom boosts the speed, links up with Alba and Messi beautifully. He even assists Messi in an Alba-esque manner to seal the game
It is understandable why Valverde is desperate to keep playing Coutinho and hope for him to strike gold. They paid 142 M for him, and are desperate to see him perform.
However, no individual is bigger than the team, and if it requires replacing a 142M player with a 40M player to help the team move forward, so be it.