The Frenchman guided his side to the Premier League summit earlier in the season, but Arsenal subsequently fell away with a run of two wins from nine league matches prior to mid-April.
Since a 3-0 thumping at Everton last month, Wenger's men have recovered to win four in a row, culminating in Sunday's 1-0 victory against West Brom as Olivier Giroud's header won it at the Emirates Stadium.
After that success, Wenger praised his charges for reaching Europe's premier club competition for a 17th successive season, but conceded some disappointed at the manner in which they had dropped away in the title race.
"I believe the mentality of the team was outstanding," he told BBC Sport.
"We still have games in front of us. You can be pleased (about) the attitude, but frustrated because we were top of the league then we dropped off.
"We had injures - three or four players who missed too many games. And in some games, at the start away from home, we were caught by surprise.
"We were perhaps too cautious and not confident enough. We paid a heavy price for it."
