While I really like the unique situation in which Paladins, as a melee class, have a spell that is going to encourage a lot of people to take a large number of levels of Paladin rather than a core ability, I wonder if having a spell this strong doesn't create a problem when it comes to adding power to the KOTC tree.
In other words, Holy Sword, as it is now written, provides a buff that, from a DPS perspective, outshines (or in some rare cases ties but only for two specific weapons) all other tier 5 abilities. It's so strong that I think making the KOTC tree appetizing for more than those who just want to use Adrenalized Exalted Smites by adding decent general DPS abilities would throw DPS Paladins so far in the other direction (underpowered to overpowered) that it would be counterproductive if the objective is to balance the classes. If Holy Sword is released as strong as it is, I think it's hard to add much power to KOTC because of balance issues.
Perhaps the spell should be broken into two parts, as I believe some have suggested, with half of it being moved to tier 5 of the KOTC tree. If the +1 multiplier part of the spell is moved there, Holy Sword, assuming that the +1 crit expander amounts to a +2 after Improved Critical like all of them do with the exception of in the Ravager tree, will still be an amazing spell - as powerful as the T5 Ravager and Fighter abilities (classes that should out DPS Paladin). The +1 multiplier on T5 of KOTC immediately makes the tree great and going T5 fully becomes worth it for anyone intending to DPS, not just those wanting to lock themselves into Fury Smites, which again, are going to be amazing, but the tree should be appealing for more than just that.
Players are always going to want more. The trick when dealing with player feedback is to separate objectivity from biases to save oneself to being locked in a constant cycle of balancing. There have been some requests and suggestions for more Paladin power in this thread that have frankly been head-scratchers.
It doesn't matter whether the feedback is coming from a small council, lamannia testers, or the general forums, there are players in each of these settings that will ask for as much as they can possibly get. There's often very little objectivity when one is looking at an opportunity to buff their favorite class or if they spy a potential build option that they think will dominate, and players will ask for power that goes way beyond anything remotely reasonable to make these things happen. A hundred heads are indeed better than one, but player feedback is a double edged sword and separating fact from fiction is a daunting, but necessary task.
When it comes to adding power to classes, erring on the side of caution means not having to be stuck in an endless cycle of buffing, class by class, which ends up being the only option because the community generally doesn't tolerate nerfs. If too little is done, a little more can be added. However, if too much is added in the first place, it generally stays out there and everything else eventually gets adjusted up, which seems like a lot of work, although I could see how shifting the class power balance every three months could keep some players playing the game as they continually pursue the latest power-gamer option. By the way, breaking the Holy Sword spell into two parts wouldn't be "erring on the side of caution" or "doing too little". I don't want to give that impression. There's plenty of power in Paladin even if the parts of the spell are moved to different locations. In fact, there's probably too much power being added in total even if this change occurs, but at least it prevents the need to add any more power to the KOTC tree.