2400 certainly sounds impressive, but the bonus is actually smaller. 2400 mana points from smaller increments isn't the same as 2400 regular mana points. In other words, the efficiency of spending these 2400 mana points, obtained "in portions," isn't very high. I'm not arguing that Logu shouldn't be taken, but hero upgrades are statistically predictable, so sometimes you can take a risk and forgo Logu in favor of a more useful skill *at that moment*. There is a risk, of course, but it is predictable.