On my previous car, a 2003 Acura TL, I had both the Primacy and later Premiers on it.
Both are excellent tires. Capable in rain and snow.
The Primacy's lasted for 40K and there were never any balance, or uneven wear issues. This was the first tire that really tamed my TL in the snow. The large V6 coupled with traction control that was minimal at best, caused this car to be one of the worst I have ever personally owned in the snow (you folks with the 270hp V6 in your Camry have my sympathies, if you have to drive in the snow). With the Primacys, I could finally venture out in snow with some confidence.
The Premiers seemed to be noisier the first 3K, but quieted down to the Primacy levels. A smidge better in deep snow and stayed extremely capable in the rain, even with 40K on them. Had the transmission not died in it, I fully planned on driving that car with those tires through this winter, even though the tires would have had nearly 45K on them by now. I live in Wisconsin and we get real snow up here.
My Camry, a 2014.5 LE, came with the Michelin Energy tires and I got my first experience with them in snow this past week and they are extremely average. Not as bad as I feared, but I cannot see using them for more than just this one winter. They currently have 12k on them. Performance in the turns is abysmal, as expected. Considering this is a tire centered on efficiency and not performance.
IMHO: Premiers are the better tire over the Primacy, especially in the long term.
My experience with Pirelli in the past has always been they produce great, but short lived, tires. Similar to Yokohama. Absolutely great performance, for about 20K, after that your results may very. Some of the reviews on Tire Rack bear that out on the P7, but there are many that are reporting exceptional tire life. I would be open to buying a set of P7's, but considering I can get Premiers from Costco much cheaper, that is the route I plan on taking, when the Energys work my last nerve.