A single Zee-lixir isn't a huge deal as the effect on zombies is only 1.5 seconds long. It's when several wizards use them in quick succession that it becomes a serious issue. A wizard riding a wizard and them using their zee-lixirs one after the other can make that last 3 seconds and more can extend this further. The cooldown is 20 seconds I think (can't confirm right now) so it's throwing all your eggs in one basket but it can certainly work at a key moment
They may need to add a kind of debuff where you can't be affected by more than 1 in a 10 second period or something like that, and perhaps it shouldn't be such a cure all like it is now.