The phrase "overwhelmingly from" is correct and can be used in written English.
Example: The donations to the charity were overwhelmingly from local businesses and individuals.
Over all, it is overwhelmingly from the Deep South.
Whatever revenue Newsweek attracts comes overwhelmingly from the printed product.
But those genes have come, overwhelmingly, from male Indian cattle.
The rioters came overwhelmingly from these postwar estates.
Let's not make a false pretense of balance: it's coming, overwhelmingly, from the right.
This year's record crop came overwhelmingly from Helmand, as well as other embattled regions.
However, the British recruited overwhelmingly from the north for the armed forces, police, and paramilitary forces.
Those who voted against Putin come overwhelmingly from the middle class — still relatively small, but growing.
But the dangers of Aceh come overwhelmingly from the army and the paramilitary police.
Currently, students who score over 80 come overwhelmingly from high SES backgrounds.
"Today they are overwhelmingly from customers trying to take advantage of new features of software".
