The IS-2 scatter isn't from the drunk driver but the inaccurate 122mm gun that was rushed through production.
This had 2 causes:
1. German tank cannons have better aim system
2. After firing one shot, the IS's gun had to be brought in the initial position in order to be loaded. So the crew losed aim. Then, after loading, the crew had to aim again.
There was a joke:
Once, in the war commission, Stalin expected new solutions from his soviet tank builders, because the german tanks were clearly superior.
Ivan, tank construction expert at a soviet tank factory, says: Comrade Stalin, I have a proposal through wich we will reach the german technology and be on pair with it.
Stalin didn't look to pleased and said nothing.
Seeing this, Serioja, tank construction expert at a second soviet tank factory says: Comrade Stalin, I have a proposal through wich we will overpass the german technology and we will clearly be in front of them.
Stalin begun to smile, finaly satisfied.
Seeing this, Ivan stood up and said: Comrade Stalin, I strongly suggest not to overpass Germans, because they might see our ass ripped pants!
Stalin didn't listen, threw Ivan in gulag and built the IS tank.