Anyway, I'd say we're better of comparing spells as they would be on Tuesday, which takes the cast time out of the equation.
LB: 1271 + 73.9% -> 2161 + 125.63%
LvB: 1579 + 100% -> 2369 + 150%
The -> conversion is adding Shamanism for LB, Flame Shock for LvB. As you can see, even without factoring in the auto crit function, Lava Burst hits harder and scales better than Lightning Bolt. The reason your math was faulty was that you were comparing the damage of a 2 second cast with a 1.5 second cast, without taking the time difference into account (note: spellpower coefficients on spells used to be based on cast time / 3.5, and most spells that currently differ from this have only been tweaked slightly, so it's impossible not to consider time in this context unless you can eliminate it with identical timeframes).
Pretty much everything in the Elemental spellbook has a higher DPET value than Lightning Bolt, which is why it's used last.