Can I disable pinch to show all open tabs in Safari?
You can disable this feature in Safari, but it will also disable "Zoom in or out" in all other apps.
System Preferences > Trackpad > Scroll & Zoom
I actually had to check the "Zoom in or out - Pinch with two fingers" box to even figure out what you were talking about.
Limitation: This disables the gesture in more places than Safari.