Lions are similar to electricity in the way that they are both symbols of power, this is why Luxio's typing makes such sense. All through history, cultures have depicted lions and have been symbols for kings, countries, and even religion.
There is art from Mesopotamian cities with elaborate carvings of lions on stone faces. They were symbols of power along with bulls and eagles. They would combine these powerful animals together to create chimeras that represented the power of the king. The lion's influence as a creature of power is also found in ancient Egyptian artwork. The goddess Bastet was a lioness as well as the goddess Sekhmet. Sekhmet, notably, was the goddess of war.
In medieval times, lions were shown on flags, tapestries, and paintings. Lions were symbols of powerful kingdoms. Lions were also depicted as powerful Christianity. In many portions of the Bible, Jesus is referred to being a Lion (as well as a lamb). But the lion represents power and strength.
How do these symbols of power tie in with Luxio? Why is Luxio a lion? Because it is also a powerful creature! And what better to represent power that that of a lion, as human beings have been doing for centuries. Discussed previously, Luxio has a high attack base stat and in the Pokeathalon is very powerful, hence why the link between lions as symbols of power are crucial to discussing the abilities and design of Luxio.