What the Hell are you talking about? There are a selection of different fonts and you can control the size of the fonts.
I was wrong about the fonts. Been a while since I ran Kindle on my iPad. But there are a couple of things that make reading more difficult and there is nothing we can do to fix things.
The margins are very large and very annoying. On an iPhone it's abominable. On an iPad it's not nice.
The line spacing is huge and we cannot fix that. On an iPhone it looks stupid and on an iPad it's just very annoying.
Kindle wasn't made with users in mind. It was made so you'd get fed up of using the poorly designed app and move to an eInk Kindle.