I used a Sony A6000 for a number of years, a few months ago I changed to micro 4/3rds and I have a GX8.
The Sony A6300 is an improved version of the A6000 I had but certainly close enough for me to have views on this.
They are both excellent cameras and capable of great image quality especially when used with top quality lens.
You will only see an IQ advantage with the larger sensored Sony at high iso . . . say iso3200 ?
The big advantage I see with the GX8 and the prime reason I changed systems is the range, quality and price of the lens available for each system.
Pair the Sony with the Zeiss 24mm f1.7 (E mount) and the pairing is capable of capturing superb images, however the Zeiss 24mm is approx £800.00 new. I have shot many thousands of images with this combo, and I miss it.
There are other excellent lenses for the Sony A6000/6300 but they are not abundant, will probably cost more then the equivalent m4/3rds lens and in most cases will make your 'payload' bigger and heavier.
Yes there are some small lens available for the A6300, I'm thinking of the 16-50mm f3.5-5.6 (kit lens) the 16mm f2.8, the 55-210mm f4.5-6.3. I have owned and used them all, they are 'consumer grade' and will keep many users happy with their quality. However the A6000/A6300 are worthy of much better glass.
The range of lens available for the GX8 (and all m4/3rds cameras) is awesome. Not just from Panasonic but Olympus and Sigma and Samyang etc.
The 'kit lens' options are really tiny and lightweight i.e the Panasonic 12-32mm f3.5-5.6 and the 35-100mm f4-5.6. The quality of this pair of lens is a fair bit higher than the aforementioned Sony options. My opinion, yes but many others concur.
Prepared to spend more for higher quality ? the professional grade Panasonic 12-35 f2.8 and 35-100 f2.8 are top quality, much smaller/lighter than apsc, not cheap but these lens are far easier to find used than the Sony equivalent.
There are many top quality really small lens for the GX8. I own the Pan 20mm f1.7 pancake, the 30mm Pan Leica f1.7 and the Pan 42.5mm f1.7, Again super quality, very small and lightweight.
I do not understand the science but it is well documented that it is easier to design top quality glass for the m4/3rds system than the larger sensored cameras.
Remember the GX8 has internal 'anti-shake' so can be used with all Olympus and Sigma lens which do not have onboard lens 'anti-shake'
The GX8 is built like a tank, is weather sealed and has the superb oled evf that not even the latest GX9 has.
I sure you would be happy with either the A6000/6300 or the GX8, I know I was.
Happy shopping.
p.s GX8 'Shutter shock' often talked about, I have never seen it and many other reviewers haven't either.