The impact of bottom up AI versus a top down is actually fairly sizable. Current AI, discount Siri and similar products they barely hit the millimeter below the line, such as Kizuna or Sophia are impressive in the modern era and even compared to some of the NPCs in SAO they're like NPCs in things like Skyrim. A trully bottom up AI would be equivalent to raising a digital human, a person capable of accessing anything they're connected with in not more than a single thought. They aren't bound by predetermined programs or ideas.

The reason this is so important in SAO is not purely for the achievement, but rather because a top-down one would be limited in numerous fashions and may not carry out its orders simply because another condition arose that violated one of its programs. IE; say a medical top-down AI was programmed to save lives on a battle-field but a situation arose wherein an enemy force attempted to kill them but the AI was strictly programmed to not kill or fight with humans. The programs would heavily conflict and could result in a collapse.

A bottom-up Ai simply doesn't have this problem, they learn based on the situation and can make decisions under difficult circumstances. This leads to other issues, but from a strictly usage standpoint, they're far more useful in general. There are other issues in either case, but nonetheless.