Forget Devoted Spirit's healing. This is the school that lets you hit enemies so hard they can't attack your allies, make AoOs even on 5-foot steps (and possibly against tumbling enemies), make all attacks against anyone other than you take a fairly large penalty, and take 11 on any roll. The healing just makes it so that when you do get hit (it's your job, after all) it doesn't put you down. These are all things that make crusader the only viable tank in the game.
When you add in White Raven it just gets better.
I'll grant you that natively crusaders have somewhat dissynergistic ability score requirements, but remember that ToB is very dip friendly, so dipping Marshal for Charisma to initiative, Bard for Charisma to Attack, or something similar is absolutely feasible. And of course you don't get a ton out of Charisma natively, allowing you to focus entirely on the physical stats if you prefer.