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The big thing for me is the talent IMO. None of those comps were as highly rated as Upton.
Home/Road can get blown out of proportion, especially for high-end talent. I remember when Soriano was a sub 700 OPS guy away from Arlington for several years and actually got better the second he left.
WAR includes park factors. Upton's 5.6 WAR in '09 as a 22 year old MISSING 20+% of the season would have been the 2nd best year in A-Gone's CAREER.
A-Gone never even had a 4 WAR season until his age 27 career year.