[MarkJerling]

I beg to differ.

The "feather" detail in the little bird looks pretty good to me.
The galvanised water tank at top left of the second image is tack sharp.
The in focus bits of the third image are a bit dark and low in contrast, but they look OK too.

Remember that at close focus at 300mm depth of field is still quite thin.

More testing is required - preferably using a flat subject perfectly parallel to the camera's sensor and focussed in live view on a tripod.

I agree. All three photos, in fact, have areas that are sharp. But, shallow depth of field is causing large parts of the images to fall in the out of focus areas.

[Vital-Blurs]

Great pic, and certainly sharp enough. That lens is definitely best under bright lighting.

I used to race those little buggers 25 years ago!

It's come along way since those days. Mostly in terms of ease of use and durability, but LiPo batteries, brushless motors and 2.4GHz radios have removed a whole lot of headaches, although some things never change