Age of Kings campaigns more difficult than they should be?

Younger me played the original game a lot, mostly battles vs AI but also clearing the campaign a couple of times. I remember these being very easy on standard mode. However, recently started playing the HD version, and a couple of levels were quiet the challenge. Not that that is a bad thing, but I've got a feeling it is a bug, and I've been playing the campaign on hard. Mostly struggling for resources as the opponents kept attacking, failed 'Into China' twice for being to slow (I am a turtle though). My towers and castles were getting sieged a lot during the campaign and attacking any of those brought the cavalry out.

Cleared everything, and I liked the challenge, but now I'm clearing The Conquerers, and so far everything has been way too easy. The AI isn't even trying unless it is scripted. Attacking a castle, tower or TC hardly brings out any opponents, I'm rolling trough the campaign (currently cleared Atilla and El Cid). Not trough any sort of skill, just the lack of opponents.

So my question is, is there a known bug that 'standard' is actually 'hard' for the original AoK campaigns? Or is there something wrong with The Conquerers campaign?