1) Warlords are leaders. That feat makes warlords a worse leader, as the prerequisite for turning Brash Strike into a leader power (being free attacked) comes up less with the feat. (Bravura warlords are a bit tougher than "classic" warlords anyway. If the player is afraid of getting clocked when they use that power, they should use another power that turn. Or not play a bravura warlord.)
2) Tanking isn't about being tough. Being tough is a requirement to be a tank, because you draw heat. Warlords have no ability to draw heat or punish enemies for attacking their friends. Being tough for it's own sake is just about raising your power level, and in this case it also weakened your leadership ability. In other words, simply being hard to kill doesn't make you a tank.
I maintain it's a bad feat for warlords. I'd as soon take a feat for rogues that boosts their AC by a lot for a turn, but inflicts the weakened condition on them for a turn. It does the same thing; exchange your primary combat role in exchange for not dying.
Harlequin Style is far from the only bad rules element in the bloat, and there were bad things in previous edition bloat too, but when the bloat gets that bad, it's time to bow out with class.