Can't help you with the A9ii, but my A9 with the sigma adapter works well with most of my Canon lens. The EF 70-200 f/2.8Lii and the EF 100 f/2.8L have minor issues at times both on the A9 & A7Riv, but more so on the A7Riv. A9 works better than the A7Riv with Canon 100-400.
My standard Canon zooms and primes work fine with the Sigma adaptor and both bodies.
If I were an action shooter or serious BIF shooter, I'd bite the bullet and go native FE on the long lenses. I'm not, and I'm cheap, so I don't see myself selling off my Canon lenses and going native Sony E mount.
OTOH, if I can get my motorcycle sold, I'll probably pick up an FE 200-600.
Thank you for sharing your thoughts.





It would look 99% worse without a colourful sky. Thank you for the comment though 
