My main worry with evaluating 6th men types like Harden is not necessarily that they benefit from playing next to superstars, but that they benefit from playing a ton of minutes against bench players, inflating their stats.
This is true, but the biggest IMO is just that teams in the regular season just don't waste their time coming up with schemes to slow the #3 scorer on a team. This is one reason Harden's struggles in the post-season is a concern - the level of preparation for the playoffs is much higher.
So, we'll see, but I don't think anybody could have asked for any more out of Harden's debut.