4Game

TL;DR – Peeker's advantage always exist as long as there's ping involved… BUT Peeker's advantage is only affected by the camper's ping, not the peeker's ping. Peeker's ping has nothing to do with it, and camper's ping only affects the camper negatively. In conclusion, your own ping can never be utilized as an advantage.

Edit – I just found out my theory is correct as per https://www.youtube.com/watch?v=FVV_GHVXYzI.
It won't change the minds of people who want "foreigners off of our local servers" though.

I will not go through basic explanations of client-server relationships.
Please read only if you know what pings really mean.

Excel version you can play around with the numbers : https://docs.google.com/spreadsheets/d/1kB7d5iwIYqcNdcbOeWYGCP15iNGX3VpZw_m0LZm8yjI/edit#gid=0

Consider the following scenario :
Y has been camping a room, and X rushes around the door, entering(peeking) the room.
Both X and Y shoots each other, and X kills Y.
How does ping really affect the outcome here?

Let's say that from the perspective of X, the moment X entered the room is defined as a global timestamp of 0.
From the SERVER's perspective, the timestamp at which X killed Y can be defined as X's reaction time + X's ping(the delay of X's kill to arrive to server).
In contrast, the timestamp at which Y killed X will be defined as Time at which X was visible on Y's side + Y's reaction time + Y's ping(the delay of Y's kill to arrive to server). We know that time at which X was visible is equal to X's ping + Y's ping.
Therefore, we are comparing X's reaction time + X's ping vs X's ping + Y's ping + Y's reaction time + Y's ping.
X's ping both exist on each side, so we can remove it from the equation.
Then we're comparing X's reaction time and 2 * Y's ping + Y's reaction time.
As you can clearly see, the peeker is only benefiting from the enemy's ping. Higher the ENEMY's PING, more breathing room you have on your own reaction time/TTK.

Disclaimer: I haven't done multiplayer game development aside from back in undergrad days.

I'm sure actual games have multiple techniques to change the outcome above, but whatever techniques there are, I am doubtful that it would intentionally somehow make high ping more advantageous, considering that by default high ping can only be disadvantageous.

I'd love to be proven wrong.

Edit: This is a separate discussion from desync which is purely a server code/performance issue aside from client pings. When there's desync involved, completely regardless of ping, the peeker's movement will not be properly relayed to the camper's game on time(again, completely independent from ping). This means that peeker will be massively advantageous, because peeker's position being out of sync on camper means camper will see the peeker much later than the theoretical "X's ping + Y's ping" timestamp.