For those who aren’t familiar, the addon (and similar ones) will immediately tell you when a horde/alliance is within render distance without having to be a hunter with tracking or anything of the sort, alerting you instantly to where they are, what their name is and even plays a sound notification (a special sound if it’s a rogue or druid it detects). As of right now the only way to avoid detection by someone using it is to take no action (any ability, item, canceling any buffs, attacking, etc). It does this using the combat log.
The problem here isn’t to do with balance, it doesn’t matter if people were able to do something similar in the past using the combat log and the fact that everyone can use the addon is irrelevant. The addon detracts from and changes how world pvp works, whereas before you could hide from or ambush the enemy using the environment (heavy foliage, deep in the water, behind a hill out of line of sight, etc) now the “world” may as well be nothing but a geometric flat space with all objects unrendered. The addon is anti-skill and dumbs down PvP, you don’t have to pay any attention to your surroundings just mindlessly wait for the addon to alert you with it’s 360 degree Superman vision.
No addon should be what shapes the meta. In the past (or is it future in Classic’s case?) Blizzard has intentionally broken the functionality of addons that do this (e.g., the addon in WOTLK that allowed you to draw objects in the world that others could see, the addon that facilitated premade queueing in battlegrounds without queueing as a group and thus facing other premades, and others).