If I remember correctly about the original releases (AoE1 of 1997-1998, AoE2 of 1999-2000):
On easier difficulties, AoE2’s AI is handicapped in its behavior more than AoE1. So if you leave an AoE1 AI alone *and* it doesn’t suffer from some issue that disables its expansion, it will build a sprawling empire regardless of difficulty, while the AoE2 AI’s expansion & aggression are slower and more limited.
So in this sense, the original AoE1 AI is indeed harder than original AoE2. However, for a slightly experienced player, it is also extremely vulnerable to early aggression and exploitable.