I've been a Canaanite T2 player for years, and can tell you they work perfectly fine by themselves. They work best, though, with an offense that doesn't mind getting negated (I pair them with Judges for that reason and for the fantastic synergy with Canaan-Ehud or Abimelech-Gideon, but Prophets are another good example).
And that's really the key, all defenses work fine by themselves but you really want to pair them up with a good
offense to make them work. With many copies of the best cards in a theme, there is no real need to mix-and-match (in fact it sometimes hurts you). Now, if you are running Phillies without at least Lot's Wife, I have some serious questions for you, but they run just fine without Canaanite back-up. Could the benefit from it? Yes, but I'd actually say the offense matters more.
Look at Heretics for instance. If you run them, you really better not be running
Barnabas in your deck too. Green prophets are juicy (and easy) banding targets, and he CBP wrecks your own defense. You also don't want an Isaiah deck that runs Covenant with Death either, since that is one of the few things to shut down Creeping Deceiver and it also hurts your other CBI heretics. Instead, consider pairing them with something fast and NT so that both sides can use Herod's Temple. Heretics aren't fast (beyond some Dreaming), but they can be hardy if you get them out with their support in Wolves, Temple, CP, Chorazin, sites for locking, and so on. So a drawing offense here can really set your defense up for a solid game.
So honestly, I feel that adding splashes to defenses in T2 is not necessary in most cases unless they REALLY synergize. Demons and Magicians, for instance, love working together (as only makes sense). Other decks though fight over resources (deck space and hand space) and you can use the 'best' of each theme, so why not focus your energy?
Instead, I feel that the offensive choice is more important, and it should complement your style of play on defense, take advantage of what your defense does, or do something that helps your defense's board presence.
