Trouble with Button "Hold" Delay?

Ever since I started playing, I've had difficulties with triggering "holding button" keybinds (heavy melee and zipline specifically). It seems like the time needed to trigger these things is significantly shorter than others' I've talked to. I frequently heavy melee instead of light melee when pressing the button for it, and use the zipline instead of jumping/double jumping. It's not my keyboard since I have my melee on a mouse button. And I would think it's lag if it wasn't so consistent since my internet is decent most of the time.

Has anyone else had a problem with this or know what could be causing it? Is there anything I can do to attempt to fix it?

I've never had this problem in any other game before.