The ancient ruler of Scorpio was Mars and many astrologers still look at Mars as the Primary energy.
The God Pluto rules the Underworld. His other symbols include the phoenix, and the spider. Death is his dominion. His name comes from the Greek "Plouton" meaning deliverer of the womb. He also rules fertility.
As Mars is proactive, perhaps Pluto suits Scorpio better in that they seem to want control in a subversive way. The transformation in the Book of John talks about the Scorpion giving birth to the Eagle. Like the phoenix who dies to be reborn. This is, of course, the ultimate power.
The spider weaves his beautiful web to trap his prey. It is about the Time it takes that is so Scorpionic.
Life is a riddle that we all are trying to solve before we die.