If someone can apply it within the first 3 or 4 turns they are basically guaranteed to win...
First of all, to even apply it in the first 3-4 turns, you are forced into a duo with light, time, entropy, gravity, or water, or maybe a rainbow. None of these are gamebreaking combos.
Also, neurotoxin is slow. While damage does begin to pile up, 3-4 turns is a lot against a rush deck, which will easily beat it before neurotoxin gets too bad, and so will a reasonably fast domination deck. Stalls also fare well against it, because massive amounts of healing, especially light wih miracles and sanctuaries, can slow it down considerably. Neurotoxin is very difficult to use effectively without some form of control to stop from being outrushed, and/or some form of additional damage to make it good against stalls.
One final thing to consider against neurotoxin is not playing any more cards than you actually need. Excess pillars can be kept in hand longer, and prioritize higher-cost, higher-damage creatures over lower ones. These will slow the poison and give you a bit more time.
Don't get me wrong, Dunes are powerful, but they are far from insta-win.