There are very few stats that have been adjusted to the individual player yet. All players have been given a target and a template to fit their style. Thats why individual stats might be a little of, but overall I think it have worked great. This will change over the beta period, but #1 focus have been to give players stats at all.
Regarding stars, I assume Seguin have been considered to have more defensive potential then the others. Cause they have all same (almost) offensive potential, just that Seguins defensive skills are higher and that's why he is considered a 5 star. Even if it looks wrong (in stars) I think it's pretty real.
RNH
of ability: 800 Def: 675
Hall
of: 815 def: 640
Yakupov
of: 815 Def: 610
Seguin
of 815 def 735
On Schultz he looks to have great offensive d-men potential, dunno why the game gives him so few stars.