Brazilian Massa has driven for the famous British team since leaving Ferrari, but he says that the immediate impact of the arrival of former Mercedes chief Lowe this year was palpable.
"What he has done is unite the different departments," he told UOL Grande Premio.
"Before, one area would fight with another because a part was taking time to be ready, for example. That has changed. Now the areas are united in the right way, just like a big team."
Yet the 36-year-old said that Williams are still lagging behind the really big teams in other ways.
"I think we cannot compare on the financial side, as there are a lot of things that make the difference between a big team and a middle team," said Massa.
Williams are sixth in the constructors' standings ahead of this weekend's Monaco Grand Prix.