A job doesn't need to be preferable over another for X fight to be balanced. As long as all tanks can clear the content, then all tanks are viable, which is all that's really necessary. The problem was that the disparity in DPS between PLD and the other tanks lead to PLD being unable to clear content in the same gear that DRK/WAR could. PLD, with the current gear available (especially in 3.1), can clear everything. If played correctly, they won't be holding anyone back because the DPS check will be met. Yes, DRK/WAR makes it easier, but that doesn't mean it's absolutely necessary to bring DRK/WAR atm. During early progression, yes - but now? Nah.
In terms of clearing content, PLD itself has no problems atm due to the gear boosting it's effectiveness to "good enough". In the future, in 3.2, PLD could face some troubles if we have the same strict DPS checks... however, based on the information we've been given, it sounds like tank DPS as a whole is being reworked and we could see even larger sweeping changes to the meta.
Basically, the TP change right now is fine. A DPS change isn't actually needed in 3.1 as it will have no effect on PLD's current ability to clear a fight. PLD can, and has, cleared everything now.