I'm not an expert, but based on anecdotal evidence as well as what I was told by a specialist as a kid, Dyslexia technically is just the symptom of having difficulties with reading and/or writing. People will often have multiple "dys" conditions (not sure of the names in English, but difficulties speaking, with math/numbers, with orientation, with one's understanding of their position in space, etc.).

I forget why, but we often bunch all that together and put it under the dyslexia for ease of use when it concerns language/learning. And it's a clearly identified condition at that stage; that can be transmitted genetically (mostly by the father IIRC).

On one extreme, I've met people who could barely read at all, and were totally unable to write with a pen because of dyslexia; but I also know people who technically have common issues linked to it (slow reading, confusing similar letters, etc.) but would not qualify for a proper diagnosis because it is too mild to affect their life in an adverse way. So yeah, it's one of these things that falls on a spectrum.

As for OpenDyslexic, I find it too "wonky" and lopsided. It almost feels like the letters aren't sticking to their line. To be fair, that's how I write, but it doesn't mean I want to read wobbly text.

Atkinson Hyperlegible, on the other hand, helps a lot with things like l,p,q,i,j,I all having clear distinctions that help make words easier to understand.