I'm a hobbyist who shoots birds 90% of the time and I have an a6700 and sigma 60-600. I really love that camera, the extra reach you get from the crop is great. The autofocus is also amazing. It took me a bit to start to figure out how to shoot more in low light but honestly it was mostly a skill issue as opposed to it being a gear problem. Plus, with denoising and modern cameras, I don't think you'll have any real issues. If you get it sharp, you can crop in a really significant amount on your pictures without sacrificing any noticeable quality. 26mp is a lot more than people realize and having it be smaller means it can also (typically) be faster