Here's a better question. What would you like spotting scopes to do instead of what they do now?
there are multiple options to balance them.
For example -as mentioned earlier- add a delay between standing still and the ability taking effect
...or remove the permanent part of it and change it so scopes unlock a timed ability that costs munitions (similar to vet 1 ability of ZiS3, SU76 and SU85)
...or change the ability completely and it now grants additional maingun accuracy while standing still, instead of additional sight.