"Stubbs had a off year last year but I wouldn't say Choo would make their outfield significantly better"
Well you're wrong because it does make them significantly better. Stubbs is nothing but a fourth outfielder who strikes out a ton. Choo would make their lineup so much deeper.
That seems to be what's expected:
Reds get: Shin-Soo Choo and Jason DonaldD'Backs get: Didi GregoriusIndians get: Drew Stubbs and ARI pitcher