Regarding the sample Heretek - I would never call him either whiny or a loser, especially not by virtue of his graft being inferior to Astartes mutations.
First, as others have pointed out, he's unlikely to have tried the best stuff on himself, because he's quite reasonable in his madness and wouldn't want to end as a Spawn by accident.
Second, he got captured in the middle of his research, and we don't have a slightest idea what he had accomplished other than on himself, or what his end results would look like.
Third, even if it's currently inferior to what Astartes have, merging his own flesh with that of a daemon and coming out intact and tougher is nothing to balk at, considering we're talking about a starting character. In fact, it looks pretty awesome to me. Of all characters in the demo, he's the one that gets me most excited about character building options in the full game.