You know, as with everything, I think this is all personal preference. I would hope that panelists view the player as the player they were that year, but I'm not sure anything can be done to force someone away from their decision if they take over matters into consideration.
For instance, if you use Bernard King of 1983-84, well that year may have been the single most spectacular year a SF ever had. King was near unstoppable averaging 28 points on 18 shots and in the playoffs he was even more amazing. But years before that and years after that, after he hurt his leg, he was never the same. But that one year...that is what should be considered. That's what I would want to be considered. But other than two years in his career did King ever exhibit he was the type of player to be relied upon to be that leader, to shut down opposing players, to be that clutch #1 guy? Not sure he was and because of that some people may take that into consideration if comparing him to someone like Dominique Wilkins who did what he did for over a decade.
I can't stop panelists from having a different view. I can't stop people from looking at a player's whole history and letting that influence their voting decisions. I just can't.
Its one of the reasons I would like to revolve the panelists every year so that we don't get stuck with just one set of ideals of what players are.
History can be interpreted in many different ways depending upon the perspective of the individual looking back at history. For that reason, I would want the panelists to attempt to view the player on the team in the light of the year that the owner chooses but if the panelist has some perspective of the player due to their historical view of the player then I really can't stop that from coming out in how they vote or how they explain their vote.
Best I can tell you is make the best team you can and feel comfortable with it because its going to be a great team, and then let whatever happens with the panelists happen.