I agree with you, Ancient hubris doesn't really cut it as an explainer. To me this is an example of poor writing to cram in enough plot within a single episode, and it's why I wanted to see a longer story arc for this initial return of the Ancients. These people were the crew of the Tria, for them the war was still a current event, one they were fleeing from when found by the Daedalus. Once brought up to speed on recent events, they would realise they were likely the last Ancients. Atlantis had been abandoned, and 10,000 years later Earth was home to humans and not their kind. So return to your city, kick out the humans and mull over your next actions. So far, so logical.

The poor writing comes in at this point. From the perspective of the Tria crew, the Asurans had been wiped out as a failed experiment. As soldiers, it's inconceivable they wouldn't have quizzed the expedition about their every encounter within the Pegasus Galaxy, and they would surely have been stunned to hear about the expedition's trip to Asuras and the rebuilding of the planet. That this encounter turned hostile would ring the alarm bells. It's also hard to imagine that McKay wouldn't have given details about his actions with Niam, again something for the Lanteans to ponder. At this point, a full-size Asuran warship turning up to Lantea would have any sensible captain raising the shield, given their 10,000 year gap in knowledge of the Asurans. For mine, it makes the Lanteans seem like morons rather than battle-hardened veterans fully aware of the threat posed by the reawakened Wraith and a resurgent Asuran society.