I'm hopeful with Dias it's more an integration issue than an ability issue. Same with Aké.Yes, our defenders generally make a high percentage of their pass completions because teams generally back up and pack the bus against us. So how good a passer our central defenders are isn't wholely discernible from their pass completion %. Seeing as 90% of the passes they make are simple and sideways.
It's no surprise most of our defenders have pass completion rates in the low 90s.
That said, when watching our Central defenders ( Barring Ake who I haven't seen enough of in our system) I believe Dias has the weakest range of passes and the weakest at breaking the lines with his passes. John, Eric and Garcia are superior technically, and probably Ake too.
Even today when Fulham somehow convinced themselves to press us. It was Dias who got the most intense chasing. I strongly suspect their fishes had reached the same conclusions I did.
Although as you say, he's fine as is and is only going to improve. He's been slightly more adventurous than when he arrived so hopefully that's a sign of things.