Can you name a character from mythology who can throw lightning bolts or fireballs and isn't a god?
Confirmation bias error - mythology is primarily about gods in the first place. Outside of Greek/Roman myth, how many mortals from mythology can you name at all?
My point is that what the wizard does *looks* like what Zeus does, but that's a superficial, visual similarity. That 5th level wizard can only chuck lighting 120'. He cannot do so from the clouds, or the top of a mountain. He does a whopping 17.5 average damage (save for half), at which Zeus would laugh, and the 5th level fighter will quickly and more regularly dole out with a sword.
Basically, taking into account the actual effect the wizard has on the world, what he's doing isn't all that miraculous. It looks cool, but his actual impact on the environment isn't godlike.