All but one of those guys were here in 14-15, and they couldn't beat a McDavid-less Oilers team in a must win game. I would buy the intangible leadership thing if it wasn't for that season.
They've lost a lot of leadership, but they've also simply lost a lot of talent. Also a lot of talent for nothing in return. They had all those vets, with Kopitar and Doughty coming up as the young core pushing them. Today, Kopitar and Doughty are part of the veteran group, and there's no Kopitar and Doughty pushing them anymore. It's Toffoli and Pearson.
This is a whole complicated picture. Even when they were winning Cups, they were never a dominant regular season team. Their best year was the short year, and then they struggled to get through 2 rounds of the playoffs. The current Kings, and the Kings of the previous 4 years, could not in any way do what that 2013 team did, so not trying to discount what they did that year. They weren't great though. They've always been on the edge. Then as soon as too many things caught up to them, we have everything that we've seen since October 2014. You're not the 8th seed, or down 0-3, or having to win three Game 7's on the road, or having to constantly come back from down multiple goals(which happened in the Hawks and Rangers series), without living on the edge. If you do that, and you take one too many missteps, you're going to go down. Even their great possession game was throw pucks at the net, and not really talent based. They weren't the Red Wings from the late 00's.