This skill pretty much allows ritualist to make spirit non-stop. And often turning GW into a bloody staring match. Of course the first one to give in... dies.
Now some said well they're using 5 secs cast skill. Which's a long time to get them interrupted...
1) There's usually a displacement nearby already, which you can't necessarily reach even with long bow.
2) There're often already shadowsongs in the area, which means your warriors can't interrupt them either. So bascially in their spirit farm, they can disable warriors no problem.
3) Ritualist are often at the back liner, far back, flank position, hard to reach by any mean. Without exposing whoever's coming after the ritualist to various danger from the other team and the spirit around the ritualist.
4) Killing spirit takes time about 10 seconds (if not more!) because of where they're located, the shadowsongs, and their hp.
5) Spirit has an AoE effect which makes them much more effective than monk spells in protecting teammates.
6) The only counter to spirit are signet of creation and unnatural signet.
7) Were it not for ritual lord you can easily kill spirits. Ele can spike them, rangers can shoot them down, warriors can rush them. But with ritual lord pretty much they can just keep making one after another.
I'd say at least give a +33-40% more cost to spirit spells when using ritual Lord