Yes they are all better defenders then Harper. UZR is flawed in that if you have a really good center fielder then the corner outfielders will get a increase in UZR. That's been proven. So since Harper has Span next to him maybe he's actually a bad defender instead of average?
THose guys are rated above Heyward. Are you saying since Heyward has played next to Bourn and now Upton (who has merely been average) then his UZR (factored in WAR) overstates his defense?