Iosevka is so great. Not everyone likes the narrow look. I've tried other fonts a couple of times since I stumbled on it a good handfuls of years ago, but I always come back.
Not OP, but if you look at the Hello World code example, the “HelloWorld” class is visually divided at the l’s and the o and W are glued together. Looks more like “Hel l oWorld”.
If it works for you, that’s fine. You are right with the monospaced font being limited to the boxes. Jetbrains mono uses ligatures to overcome certain spacing limits. On top of this some characters are designed to connect better to their surroundings, as the „l“ mentioned, which is not just a stroke, but connects to the neighboring characters with the top and bottom strokes.