SuperCole(Charmed) vs. Dark Willow(Buffy)

Avatars go after those that have a certain amount of power, Cole couldn't kill himself or them with his powers so it's safe to say they didn't need him to fight anything as mundane as poison. They also are not above trying to recruit Elders and they needed the Charmed ones to even complete their plans, feeling that the Charmed ones were powerful enough to at least cause trouble. They go after the powerful ones so that they will not have to deal with the annoyance of being challenged.

but they might have had to use him to fight that poision a weakness is a weakness, and with him they wouldnt have to worry about it, if it wasnt for that potion they would have owned the charmed ones and that source wanna be zankue

They needed the Charmed Ones to cast the spell over reality and that power was not even strong enough to effect the underworld. Cole could be stripped of his powers before he became an avatar and avatars can be vanquished.

Hell Illyana Rasputin as 616 Magik could kill or depower Cole with one swipe of her Soulsword.

they must have been strong enough to do it by themselves thats how they returned the world to normal it drains them though thats why they have others do that stuff for them, and we dont know of cole can have his powers stripped anymore why didnt they do that instead of having to worry about him.

The same reason why they don't use the power of three will set us free spell to vanquish every demon they have ever encountered. Stripping Cole of his power just puts it out there in the ether awaiting another host, because he killed the wasteland creature that absorbs and probably recycles demonic powers. Willow would strip his power through absorption not displacement.