It takes a few days of chasing birds with a new lens/format to start seeing its limitations.
A bird photographer’s life would be grand if every passerine would perch at the end of a moderately low, bare branch with a clear blue sky in the background. No different from people, they seek shade in hot climate, which means shooting them with less than optimal lighting, often against a mostly dim, green background.
Not even the most modern full-frame sensor handles this scenario well, especially when ISO rises even to modest levels. Fine details turn to fuzz and they can’t be salvaged. Smaller pixel pitch of an M43 sensor can cause it to appear more noticeable than on full frame or APS-C. Note that I didn’t say “worse,” because it’s related to proportion, not format.
Fortunately, image processing software over the past few years seems to have progressed at a better pace than sensor technology, which allows for cleaner details in all types of IL cameras. So then it becomes a matter of finding glass that will capture the most details.
Which reminds me: an Oly 300mm is on the way.