I found an interesting study titled Germans in America, prepared by the Library of Congress. Many of the Germans were religious groups that were other than the majority Roman Catholic and Evangelical Lutheran majority. They tended to form small, independent communities. The document says that by 1790, as many as 100,000 Germans may have immigrated to America, and their descendants made up an estimated 8.6 percent of the population of the United States. in Pennsylvania they accounted for 33 percent of the population; in Maryland for 12 percent.
There are similar documents for a variety of ethnic groups on this page (click).

I'm not ready to give up my original thesis. I have no doubt that there were settlers in North America from most European ethnic groups from the 1600s, but the mass migration of working-class Europeans didn't happen until the middle to late 19th century, and people of English and Scottish ancestry were the center of political power in the US until well into the 20th century. Manifest Destiny was primarily a philosophy of Americans of English heritage. The Americas were conquered before most of our ancestors ever got here. Take a look at the list of signers of the Constitution - it's clear that the ruling ethnic group in the U.S. was English.

-Joe-