Zeroing in Tarkov right now is just not well implemented. Even though it shows you a range, that range is only accurate for one type of bullet with each gun. Bullets with different velocities will therefore have a different zero. Now, in theory, that could be good. Having the zeroing mechanic be clicks instead of just a simplified range sounds like a great way of making things more challenging.
Now, whether or not that is a further challenge that players should endure in the game or whether it would be okay if zeroing was simplified to accurately display the range, depending on what bullet you have loaded in is a discussion for itself.
However, regardless on your stance on how zeroing should work in Tarkov, right now it's just a massive, unneccessary hassle. Not only is the number in the corner misleading, but as there is no shooting range with long distances and distance markers, there is no way of actually learning the zeroing patterns for each type of ammunition, other than risking the gear in an actual raid.