MetalCraze
Arcane
It's not that weak when you consider that we are comparing it to games from the late 90s. And as the new consoles have 8 cpu cores, it shouldn't be too hard to offload some AI processing to their own threads. So yes, I think we can expect the hardware to be up to the task. The issue is probably that it's hard to do it right programming wise. And considering that most gamers won't ever notice/care anyway it's no wonder they don't put much effort into it.
That and a stealth game should be light + geometry dependent, have true LOS. And modern games have it much more detailed than boxes of Thief 1 & 2. The more detailed objects, the further the draw distance and more of them you have in AI view that does LOS calculations - the harder the CPU load is. That's why it's either ridiculously tight corridors with 2-3 guards at once or 'Press X to crouch/stick to a box and become invisible'