I'm rocking an A9ii and when I attempt birds I'm using Tamron's 150-500, which is fairly sharp.

I think my problem with bird photography is wanting to take photos of smaller birds at decent distances and physics is simply getting in the way. For example, I was taking photos of a house finch a few weeks ago when I was probably 60 feet away. Even at 500mm, the finch still didn't fill much of the frame. I'll be posting the photo soon, but I would be amazed if it's anywhere near this good after a big crop.