WAR is no more a one-trick pony than PLD is. If you want to call WAR a one-trick pony because of IB, it's just as apt to call PLD a one-trick pony because of HG because that's the only real unique tanking advantage that they bring (they bring the utility of silence and chainstun capability, but WAR brings a helluva lot more damage than PLD, neither of which is valued for their primary purpose of survival).
WAR is also not simply valued for MT because WAR actually provides better debuffs than PLD does (SE and SP kick the living crap out of RoH) as well as significantly better damage. Neither WAR nor PLD is really the de facto best MT or OT because which is best is entirely situational. When an enemy does a lot of regular predictable burst damage, WAR is better for tanking it; when an enemy has specific long periods of sustained high damage, PLD is better for tanking it. WAR and PLD are ridiculously well balanced at the moment.
The fact that WAR and PLD are so well balanced means that you shouldn't really be seeing any cases where a group specifically desires two of either. Double PLD is just as bad as double WAR and, because WAR and PLD are optimal for different scenarios, it actually behooves a raid group to have one of each, much like it behooves a group to have a SCH and a WHM rather than two of either.
I've actually run in a number of excellent groups that had 2 WARs. The only reason that double PLD still gets some credence is because it *used* to be the optimal comp, and people don't like changing their perceptions; it's actually no better than double WAR and categorically worse than WAR and PLD. It's not to say that you should feel compelled to take both since you can basically do everything with either tank composition, but there is a very tangible advantage towards doing what the OP is.