The Swans went into the match hoping to make a statement about their level of improvement and ability to match it with some of the league's best teams.
Instead, it was the Hawks who appeared a likely top-four candidate after their run-away 15.16 (106) to 8.12 (60) victory, just their second in Sydney since 1996.
Longmire had been encouraged by his team's victories over the Western Bulldogs and Port Adelaide over the past fortnight.
But Sunday's result leaves the Swans battling at mid-table ahead of some crunch matches against North Melbourne, Brisbane Lions and Richmond in the coming weeks.
"The fact that we're still a fair way off [the top four] and we need to get better," Longmire said when asked what he learned from the 46-point loss.
"We've had a couple of good wins the last few weeks and played some really good footy over that period.
"But we know we're still a little bit off and need to improve to beat some of those teams."
The Swans actually started brightly, kicking three goals to two in the opening term.
But they were fortunate to still be in touch at the long break courtesy of some wasteful Hawthorn shots at goal.
Once the Hawks found their groove after half-time, they ran away with the match, kicking 12 goals to four after the first change.
"We didn't have too many contributors," Longmire admitted.
"I think it started in the middle of the ground, our midfielders as a group were beaten by a pretty talented midfield group.
"We couldn't put pressure on them the way we should've and we didn't get too many four-quarter contributors.
"We can be a good team if we give maximum effort for four quarters.
"If we don't give maximum effort for four quarters, we fall back into the pack.
"We have to make sure we come to play to be a competitive team and we didn't do it today."
