Guard spirit sword buffs.
Aye, i agree, such cast time is only justified if we can target the sword to be cast on a place like the symbols we cast with Sword #2 for example.
Otherwise removing the cast time is a very good idea, making the spirit sword less bad.
If Anet wants to warn people that a guardian is gonna use a spirit skill they could create a swirling sword around the guardian as long as the skill is active or has charges or something.