Also you observed a total lack of chromatic aberration.
That's easily and much cheaper corrected in firmware/software than through better but costly optical means IMHO.
For example Nikon didn't bother with correcting CA in their new 80-400 mm lens.
My copy shows quite a bit in typical situations but is easily correctable.
It was fun though shooting hummingbirds with that lens on my E-M5 manually.
On my D800E the new 80-400 mm lens focuses and tracks hummingbirds extremely well after Nikon successfully repaired the left autofocus issue. That combination now only needs a +1 micro focus adjustment.