While compared to those other three Lowball is a tedious bore, compared to Draw, terrible players have a much better chance to win. In the Draw example, the tens are about a 5-1 favorite. In the Lowball one, the two card draw isn't even a 2-1 dog. Bad players have no chance in Draw poker. Nope, and that's why that 300BB number is mostly useless, and wrong.
Bankroll is more a function of circumstance than variance.