Yeah, you aren't going to get anything close 1.200 brewing all grain. I regularly get 80%+ efficiency with normal 1.050 beers but it drops off a cliff around 1.070. Regardless of the amount of grain, the most I seem to be able to pull out of it is around 1.080...which is decent because I can easily boil down to 1.100 during a 90minute boil.
If you really want to brew something that huge you could try topping up with extract but who knows if you can even dissolve enough to get up in the 1.200+ range. And yeast...maybe with a champagne or distilling yeast you might be able to ferment that big a wort. ...or you could try to brew something in the 1.015 range and shoot for 1.21%ABV