I don't know enough about teams to really suggest a partner that compliments Doc well, as I am in somewhat of the same boat as you.
But let me relate this to tiers and in terms you can understand.
We'll take a high tier, Marth, and a bottom tier, Mr. Game and Watch.
Now, the favors are tipped towards Marth, so that means the Game and Watch has to be better than the Marth by a large margin in order to win, where as if they were both Marth they'd be on an even playing field and whoever is better wins.
It's similar in terms of teams. You need to have a partner whose style you know and you can cooperate with. But then you take into effect their character. You're going to do better with a partner you cooperate with using a character that compliments Doc more than the same person using a character that doesn't compliment Doc so much. It would also be the same if you didn't know your partner well, yet he used a character that compliments Doc really well. You wouldn't do great with him because you don't know his style.
It's like mindgames and technical skills. Mindgames are a major part of the game, but in order to open your options for mind games you need better tech skill. They effect one another directly. Same with your partner and the character he chooses.
I hope I worded that so you can understand.