This very discussion has been done to death over the logs rankings already, there are a few solutions, some more elegant than others.
First up, at the risk of sounding like a stuck record here, my suggested approach of measuring potency per second rather than damage per second gets around this, you can still incorporate personal modifiers and combos whilst isolating it from cross party buffs to keep things simple and easy to understand whilst not misleading people once they start optimising within a static.
Secondly, an alternative to the above is to focus more on a players APM, this is actually the first thing many people will look at when going over logs and is a very useful figure for quickly (if rather vaguely) comparing your performance to someone else's.
Thirdly, if keeping the figure entirely person is key, simply subtracting cross party modifiers is another way to go. Of course this means the numbers will be incorrect and misleading for someone trying to optimise themselves within a static. Not a good solution imo.
Lastly, the approach logs took in the end, just present it as is and let people do with it as they will.