It is the great number of assumptions that is the most unparsimonious. Even if I assume God, there are still millions more assumptions for materialism.
It isn't just the raw number of asumptions that matter. Quality of assumptions is more important than quantity. If I make a thousand small assumptions, all based on real-life observations, that's much better than making one huge assumption based on nothing.
(By the way, I don't even like caling God an assumption. In science, assumptions don't float around isolated in space; they're all interconnected. The conclusion from one experiment is the assumption for another. God doesn't qualify.)