If Matt Ward does every codex book, then that would also be fine. Phil Kelly also did a good job with the Dark eldar. As long as their is consistency there should be no issue. After all, if everyone has awesome units, it levels the playing field.
If he can be criticized for anything it is for making his books *too good* with multiple good builds, very few, if any, poor units. I think this is what upsets people more than anything when they get other designers [Hey Gav, thanks for the brilliant chaos 40k 4th edition book with no options] to do different books.
All the 5th ed books seem good to me, including nids [I know not everyone agrees with that point]
There are few legitimate complaints I have about his designing. Specifically marine land raiders having space for an extra marine, yet grey knights dont! I don't understand how an identical unit, in books designed by the same person can have different specifications.
Here is a horrific build for Grey Knights.
Inquisitor Coteaz
3x Acolytes w/LasPlas Razorback
3x Acolytes w/LasPlas Razorback
3x Acolytes w/LasPlas Razorback
3x Acolytes w/LasPlas Razorback
3x Acolytes w/LasPlas Razorback
3x Acolytes w/LasPlas Razorback