So, lets talk about it.
This set has the best invisibility detection in the game, you can just activate it without any costs instantly any time. Has 33% uptime: 10 seconds active, 20 seconds waiting. It has unlimited detection range.
It has perfect 2, 3, 4 piece stats for most of the Cyrodiil builds. It has as 5th piece bonus ~300 dmg on the backbar for extra backbar healing potency. This is also quite useful.
When on the receiving end invis detection is always problematic, since sometimes you just cant tell if someone used a detection and can see you. If in Cloak or when using invis pots you wont have any information about if you are detected. If you are in sneak maybe you see it sometimes, maybe not if you are unlucky. It is not reliable the opening eye thingy.
In ESO PvP you can mark players and this is an in-game feature. If you mark them, you will get alliance indicator + huge ass marker that makes the character model visible from almost everywhere since the markers are much bigger than the character and makes the whole model visibility more than twice as tall. So you can be seen behind of almost any object/terrain.
On top of that, you can use Sentry, during the cooldown you can pop a detection pot, and then when the detection pot effect is over you can activate another Sentry effect. So, you can get 40 seconds of detection without breaks, 20 seconds of it with unlimited range. So at the very worst case you would have 75 - 80% invisibility detection uptime, just a single player.
When combined with lets say Miat's addon, you can know if any new player is in your region, activate this set, mount and run around to look for the player. Since you have the marker placed on them, you will find them easily in seconds.
What is even the point of the existence of this set in this game when there are detect pots which are extremely powerful? Why is Sentry set so powerful against invisibility? And why are you able to actually place huge markers on opponent players, when positioning is one of the most important gameplay elements in this game's combat?