Interesting. I found the opposite! With a thick point you have no choice but to shape things well and keep loops open, or the lines overlap and you end up with a messy blob.
I do most of my writing giving maths lectures and preparing for them, and I do all my writing digitally (mostly on a Samsung Galaxy Note Pro 12.2, under a document camera in lectures), so I have a record of the improvement in my writing (e.g. the same lecture examples 6-7 times, spaced a few months apart each). I use the two previous semesters/years' versions in preparation, and the improvement is clear and steady. I started with fairly thin lines, comparable to a thick ballpoint, and have ended up settling on fairly thick felt-tipped pen width, like a Sharpie.
When I'm writing for myself I tend to use a thinner pen (and write smaller and more compressed together).
I highly recommend a smaller point if you're doing math with exponents on exponents.