Even Gorilla Glass 3 can be scratched. (There are corundum particles floating in the atmosphere and corundum hardness is 9 - just under diamond's 10. Wiping a screen could scratch it.)
I've always used the 3/$5 plastic protectors. (I tried Zagg, but it's no better and more than 10 times as expensive.) I'm still on the first protector on my year old Note 3, and have 2 left - for $5. Of course I don't normally drop my phone face down onto concrete or rocks. or wipe it with a dry tissue (dampen the tissue with a cleaner made for plastic screens, so it'll float the particles off - they're that small).