This is one of the main reasons I use Jitai, a userscript that randomizes the font for each item in your WaniKani reviews. When I first started reading, it took me a while to get used to the differences in the font, and I’d often get some kana mixed up when I tried looking up words. I haven’t read enough with non-standard fonts to see how much of a difference it makes, but I feel like I could get used to font variations more easily now.