Anderson has developed well in the last 2 seasons, but Miley is streets ahead of where Anderson was at that same age.
So yes, we need to keep hold of him. He's getting game time, which is good and over time he'll phase Joelinton out.
If Miley can continue to build his physical strength he will become an excellent player. He's still just 19 so that strength can come. He just lacks pace, but plenty of midfielders have had successful careers without it.