The path the lightning took, if I understand this correctly, isn't necessarily the overall path of last resistance.

At each step along the route the electricity will be attracted towards the easiest path. It doesn't 'know' that it it trying to get to earth, it just flows towards a lower resistance area than it currently occupies. It doesn't know about gravity, up, down or anything else. It just flows according to it's only rule: flow into the next least resistive object (which, most of the time, is just an adjacent bit of air).

This means the path it takes is effectively random (to our eyes, which 'know' that the objective is to reach earth) at each stage, but overall gradually a series of decisions to head towards lower resistance result in a path of continuously decreasing resistance.

The might have been an overall more direct path to earth (which might have had less resistance overall, too) but if finding it required a jump through a patch less ionised air which offered more resistance, it wouldn't be used.