I use the unstabilized 16-55 on my A6400 without IBIS. As long as you make sure to use a shorter SS it just works fine. I often take pictures of my children (1/500) and landscapes on sunny days so IBIS is not too relevant for me. The lens is so sharp that in darker conditions you can easily shoot at F2.8 for faster SS and still everything is perfectly sharp. Still I see the benefits of an A6600 but it costs 500€ more than the 6400 and this is just ridiculous.
It was never my intention to buy this camera, a6600, its completely crazy on paper, I have the Sony a1 lol. But, it was immediately obvious I wanted something smaller/cheaper/lighter as I didn't want to damage the a1 just because I thought I should use it for everything.
I could have gone a7iv and 20-70, total cost £3.5k, a7c, £3.1k or a used a7 body of some description. But when I looked at everything 24mp FF didn't seem to look that different to aps-c 24mp and 30mp of a7iv didn't look so much better and needed aps-c lenses anyway for video. I wanted ibis, great battery life and 2.8 zooms if possible, originally I was smitten by the 10-20 f4 but after a while decided to stick to 2.8, the 10-20 still appeals to me though for size and video.
So, on receiving this a6600 and even after using a demo one at the dealer I think its better made than the Fuji alternatives I was shown, X-S10, the a7c which felt slippery and the evf was even more cramped and that dreadful 28-60 lens contraption I couldn't even open it feels to me like a6600 is a misunderstood bargain. Now I've fitted the 2.8 zooms its like wow, what a great little camera.
I've been looking around to see what cameras can compete with the a6600, its really difficult for them, Sony was very clever;
IBIS, soft cup evf as standard, selfie screen, excellent (incredible) eye af, state of the art rtt, similar to a1, if a little slower obviously, best battery life of any mirrorless camera, might be wrong on that but its what I was told, great grip, easy to operate, weather sealed, good buffer for its intended purpose.
So, what really does do more in that size of camera, 500gr or less?