That opening quote is exactly what I've been saying about him since he came.
Even without the goals and assists he was one of our most valuable attacking players in terms of keeping shape, distracting the opposition, setting the tempo, and organising the rest of the team - all while allowing us to keep the ball. Our 2nd goal against Chelsea in the League Cup earlier this season, the one Alvarez scored, starts with Grealish slowly carrying the ball over the halfway line, attracting a couple of Chelsea players, then suddenly switching the pace of the game completely. The ball's in the net 10 seconds later.
See here:
Now he's added goals and assists and is one of our most important players right now.
I think people had this idea that Grealish would only become useful to City once he started banging in the goals and getting big game-changing assists, but he was already very useful. The additional goals and assists haven't turned him into a decent squad player, they've made him undroppable (and even then, he's still not that prolific). It wasn't the case that goals and assists would finally make him a decent player for us, it was the case that goals and assists would put him in the starting XI every week and make him one of our very best.