Whoa, lots going on here. I'm not sure this preceptor has the right training for the job. It takes an entirely different skill set to precept/train than we learn as nurses and it takes a lot of practice to get good at it.
Ive been in the ED for 6 months now and feel competent no matter what they throw at me but I had ED tech experience, prehospital experience, and 2 years of very high acuity critical care experience as an RN. This is after being tested with sick patients on pretty much every shift since I've been off orientation and I would still defer to my preceptor as the better nurse every time because she has a lot more experience and ER knowledge than I do (basically she is a better ER nurse than I am right now).
Our new grads get 6 months minimum of orientation with a ratio of 4:1 max, 2:1 max ICU, and then get full support from management and the hospital for another 6 months. They told our managers that 6 months might not be enough when they were where you are now but they have turned out just fine. They know what they are doing even if they didn't trust that they did. Our preceptors are not negative like yours sounds because they were selected as good candidates and trained to precept.
I guess im saying stick with it and trust in yourself and in what you know. I wouldn't give up on the ED yet, maybe just that preceptor/that ED if it doesn't improve. Also, Shehy's makes a great emergency nursing manual to help see bigger pictures and know how to treat the patients walking/rolling through your doors.