A saying from Sun Tzu's Art of War says, if you know your enemy and know yourself, and you need not fear the outcome of hundreds of battles.
If you know yourself and don't know your enemy, you also suffer defeat in every battle you win.
And if you don't know who you are and who your enemy is, you're bound to lose.
Evan learns who Seth is from many snippets of records. From his observations of his conversation with Alexa slowly.
From the existing story, Horus won over Seth not because he was stronger. But Horus was smarter. And also, Horus had a lot of supporters around him. Seth fell over from believing in his strength too much. And look at his current temper that likes to use his immense power to destroy his target. His temperament and behavior certainly did not change.
