I know I just said it to address ilovejedd's point of me needing to zoom in.
I've been researching a bit and there is another store called eBookJapan. Googling in Japanese, I found comparisons of images between the Kindle version and eBookJapan's version. You can see the particular post here:
http://denshishoseki-navi.net/ebookj...hikaku/#sec2_5 which compares the two.
Now, I tried for one file which is 66MB on the Amazon store & 88MB on eBookJapan (about the same size as the English version on the Amazon AU store), but just from the free samples, I'm unable to really make out any difference. eBookJapan might have a very very slight edge but I'm not sure if I'm being biased after having read the post above.
Other comparisons:
https://e-bookhikaku.com/wh-is-good/ebook-n-kindle
https://tsukimicoffee.com/densisyoseki_gasitu/#i-13
Overall it seems that maybe Amazon compresses their files slightly but I guess even looking at eBookJapan's version, I was hoping for an image quality near-identical to the print version.