The Challenge Cup winners, who went into the game on the back of five straight defeats, saw their season come to an end following a dramatic 24-20 reverse at Headingley.
"We weren't good enough at any period of that game to win it," Sporting Life quotes McDermott as saying. "I didn't think Catalans were great either but they were dogged throughout and exploited a couple of defensive weaknesses.
"They scored the try off Tom's error but that's not where the game was lost at all. We had at least another two defensive blunders and mediocre attack. We've been there for a while now and the players haven't been able to break out of it.
"They've been working really hard to try to turn things around but ultimately it's cost us at the end. We haven't quite hit our straps towards the back end of the year. We're not going to get to the Grand Final and it's really hard to take for everybody in the club."
Catalans will now face Huddersfield Giants in next Friday's preliminary semi-finals.