This is the same logic put forward by Ross Perot back in 1992 and 1996 and nobody bought it then either because it's a meaningless argument.
Harry Truman was a total failure as a businessman and is regarded by both Republicans and Democrats as one of the best presidents of the 20th Century.
Meaningless to some, but prior business experience in the private sector and proven executive management skill are something I put at the top of my long list of desirable attributes in a candidate for President of the U.S. Afterall, the President is the CEO of the largest organization on the planet. Prior experience as a Chief Executive in a large organization is the primary reason that Governors are elected President much more often than members of the House and Senate.
Mitt Romney's highly successful career in business is only one aspect of his leadership ability and résumé to examine that he developed further in public office (see my tagline). In comparison, Ross Perot was a one-dimensional candidate running on reducing the federal budget deficit, never elected to public office, and a bit of an eccentric to put it very kindly.