It's not just you and it's not just Zed. Dark themes tend to be low contrast gray on gray.

I usually look for a dark theme that looks good and then make a custom version with darker the background colors and brighter the foreground colors.

Maybe it's time for to start publishing high contrast dark themes instead of just fixing it for myself.

That's what I did: https://github.com/tuzemec/zedokai-darkest-machine