This is mainly an issue for tanking, but the game (TBC classic) is not functioning correctly in regards to enemy movement and attack range. Enemies should not be shuffling around if you take a single step in any direction. This was not how it was in vanilla/BC/wrath… I don’t think it was like this until legion, in fact.
Certain bosses, like the first boss in mechanar, show how bad this really is. The old strat of everyone (tank included) going on the stairs, use to be fairly easy to accomplish, because the attack range of the boss (all enemies really) in relation to his hit box use to be far greater. Trying to get on those stairs as a tank is nearly impossible now, and even if you do, he gets way too close for it to matter; so the standard strat now is the tank stays below.
That is just one easy example, but this applies to all mobs in the game right now. It is not normal that enemies move every time the tank slightly adjusts position.