Coutinho having more goals is due to to factors: Dembele's poor injury history, Coutinho being given pity penalties by Messi (Which Dembele has never needed), and Coutinho stat padding in the Copa, where 1/6th of his goals in a Barca shirt have come from.
If we look at things on an even level, and say, only look at La Liga this season, where consistency is the most important factor, Coutinho in 32 appearances has 3 less goals than Dembele, while having 6 more games under his belt. And this is disregarding the penalty (Or two, I can't remember) that Messi allowed Coutinho to take for "Confidence".
To put it in perspective, Alena, who has less than half a season with the first team as a bench rider, has 2 goals in 14 appearances, with most of those 14 being only minutes long outside of the 3 games used as a starter.
I can't tell if you're trying to put down Dembele or raise up Coutinho, but Coutinho's numbers and performances are truly abysmal and Dembele has established himself as a crucial player for us, and the vibe you're giving off is that you think Dembele isn't as important as it seems, because I don't think it's possible to even compare him to the likes of Paulinho and freaking Philippe "I costed 160m more than I'm worth" Coutinho.