Advanced statistics are very helpful in aiding your view of the game. When watching a game, you can't keep track of the play while constantly being aware of every player on the ice and their current level of contribution. You still need eyes on the game to make an accurate assessment, but if what you see is reflected in the stats, it is likely correct.
I've watched every game except the premiere against Boston and the SOL against the Islanders, and my eyes told me that Kreider and Miller have been invisible and unable to create any semblance of offensive pressure apart from 1 or 2 games. Recently I looked into their adv. stats and this picture was validated.
Kreider has played extremely easy minutes, yet the Rangers have only produced 13.4 shots per 60 minutes with him on the ice. Miller is better at 20.8 against harder, but still easy competition. Compare this to Hagelin who has a SF/60 of 34.4 playing against the opposition's best.
It's actually quite amazing that they have been able to score points at all, but they are both riding unsustainable on ice shooting percentages (26.32 for Kreider, 15.38 for Miller, anything above 10 is unsustainable for anything but 1st lines), so that will likely stop unless they raise their level of play significantly.
Compare this to let's say whipping boy Brian Boyle who has created more offence (24.5 SF/60) playing much tougher minutes, but has less points due to an unsustainably low on ice sh% of 3.77.
I'm high on both players as prospects, but neither is NHL ready at this point IMO.
I honestly don't know why they didn't even hesitate to burn a year on Miller's ELC, they could've scratched him for a few games just to see if they managed without him after his 5th game.