Daylight rings can be neutralized/destroyed by other witches. Needs contact to siphon, other witches have magic too so they can try and distract her, knock her out, use their telekinesis, etc. Distracted for even a second is harmful cause a witch can lose concentration or mess up where timing and such is vital and the other witch can retaliate. I’ve never read or seen anywhere that vervain can be siphoned( it is ingested/worn/ can be touched). Vervain isn’t magic, it is an herb created by nature, it’s a plant not a werewolf bite which is magic. There is also a flower that acts the same way as vervain but against witches (the Lobeila flower) and other herbs that can be harmful too. Also huntress’s blood acts like Werewolf venom to vampires but to witches. Also Siphoners and heretics can be siphoned by other siphoners and heretics. Yes white oak is rare/almost nonexistent but there was that bridge and sign that was used to kill Finn and Kol, Esther also made an indestructible whit oak stake.