Just take care with the date of these videos, many things changed from iCBT videos.
I will try to answer you since i am a Sadhu C2 and from my experience.
Indeed most of Sadhu skills (in C1) are bad designed or balanced, OOB for example have low damage, but you hit 3x each hit, so it is a mid damage skill, but it is really party dependent in certain situations.
I use OOB to lure a specific monster out of a badge, if possible, or to cross some barrier with Prakriti or get away from a mass of monsters surrounding me when i am about to lose my SZ.
Vashita Siddhi is best used with the attribute.
Sadhu C1 is not really worrh right now, C3 i am not sure, since i never gone there, and probably never will on my build.
I also got Krivis C1 as a filler, as others said, Daino is an utility that is really required, specially if you are the only cleric class in a dun/mission group.
Other thing is, it is a hard class to master if you have high latency (my case 300ms+).
Unfortunately, Cleric is more sided to support than to offensive class, the classes for offensive side are a mix of physical melee and magic users, not to count that you have only 3-5 skills that hit flying enemies.
I still suffer every now and then with some flying enemies, fortunately now at Druid C1 i have more ground skills to deal damage and my Zaibas and possession are always free to be used on some flying crap that may come my way.
I am almost at my R7 advancement, Druid C2 here i go, i wish IMC stop releasing stupid costumes and fix the skills lol. Its a shame most skills of Druid are bugged (Carnivore not working in grass, even tho it is visually activated, but work in combo with chortasmata, Shape Shifting work randomly and when work you can only use basic attacks from mobs and even so don’t cause damage).