How Exactly Does Crusader's Ward Work?

Yeah; that's exactly the case. B!Ike's Urvan functions exactly the same way. If you run Distant Counter with Crusader's Ward; then the only functionality you'll get is on the second hit of a Brave weapon; rather than both hits of a ranged unit otherwise. Makes it a lot more situational a skill.

Even still, running Sigurd with DC is heavily devastating. I ran into one in the arenas, and I was not expecting it, and he destroyed my team of mages. Divine Tyrfing is helpful in that regard. So if you run DC, maybe take out CW for another skill (wouldn’t know what), unless the unit runs Desperation (which a LOT of mages do).

I personally run DC and Crusader's together. How many other sword users can say they'll survive an optimal Reinhardt and kill him on the counter(assuming Reinhardt doesn't have Swordbreaker)?

It's basically Deflect Missile and Magic seal wrapped together in one B skill.

I personally prefer Vantage in his B skill as I already have another unit that skews Rein/Lyn so I don't need him to pick those fights and he can instead focus on everything else.

Its simple, if you use DC, use QR/Vantage/Renewal, if not, leave Crusaders Ward.

It would help against desperation, but if the enemy mage gets in desperation range in range, you are probably a goner anyway.

Crusader's ward is still great even on DC Sigurd for 2 reasons.
1. it makes him survive ANY mage setup or so. Desperation will not counter your plan when using him.

2. It is the skill that weight most, meaning you'll score a little bit more in arena.

Obviously, if you don't run him on your main arena team, then this skill can and probably should still be changed when using DC.