That feels like
picking on a particular isolated statistic, one that fullbacks tend to not have high numbers of, and using it as an argument to prove he's good going forward. Yes he has two goals, but as @Womp said he has no assists. Let's look at other fullbacks....
Moses is on 1 goal 2 assists, Trent Alexander-Arnold on 2 goals 1 assist, Walker is on 5 assists, Trippier is on 7 (!) assists, Azpilicueta 2 goals 5 assists... That's just looking at right sided players. You start looking at left backs too and Marcos Alonso (3g, 1a), Kolasinac (3g, 4a), Ben Davies (2g, 2a) and even our own Young (2g, 4a) who only recently switched to playing fullback, outperform him.
And that's not just using statistics for statistics sake. It's backing up what we observe with our eyes. That Valencia quite often in an advanced position will dally on the ball, slow the tempo, hesitate to take a defender on and then smash a low cross against his shins. That he doesn't really offer the kind of outlet that worries the opposition like the aforementioned players do.
He has energy, passion, he's an uncompromising tackler, a good defender and yes, I like him too. He's by no means a bad player. But the reality is, considering the team he plays for and the opportunities he has to contribute to the attack, that he doesn't do it anywhere near enough... or well enough.