The instruments on the F800 don't bother me too much but we could probably fill this thread entirely with some of the stupid shit on that bike in stock form. I would say top of the list would be rims made out of a tin foil like substance, a stock suspension that is a joke in the dirt, and a rear shock bolt configuration that without modification can bend the frame. Fortunately all these are fixable with time and money.
As to the WR 250 mirrors, there is a solution called Highway Dirt Bikes. Top of the line guards with mirrors you can tuck out of the way in the dirt.
OP - this is a great idea for a thread by the way. Unfortunately The Perfect Line has had a serious lack of descent threads for a while. Nice job turning it back up a bit.