Not all things are the same. The AI is different (from what I’ve heard), and that patch allows the player to use an advanced scenario editor, with units that in the Definitive Edition remain hidden.
Yes, the AI is different from the UPatch. AI engine improvements and script updates have been made in the Definitive Edition (even more so in updates post-launch).
The author of the UPatch (aoe_scout) is indeed a colleague of mine at Forgotten Empires.