In theory, a sniper can disable a tank.
- shoot out the gun sight
- shoot out the driver sight
- wait for crew to open the hatch because they can't see
Not true. You are in a case of ocular centrism psychological bias. You can see, so you aren't able to realize how far one can do without seeing.
Put a fold around your eyes and try to do your own routine. You'll find that it was hard, but with a little help you were able to do.
Now picture yourself as a driver of a tank, able to hear, able to feel, able to drive, able to shout, able to read maps, able to compute travelled distances because can see the speedometer, able to see where compass is pointing, able to communicate through radio.
You'll figure out a sniper with no ready anti tank support (specially if unable to call them) is worthless against a tank's crew (specially if they are able to call support).