I find this statement puzzling, and often made by people who don't own or never ridden a Sidewinder, but maybe have just looked at pictures.
I was sitting in my Garage last night having a beer with a friend. We where looking at my 2017 Sidewinder RTX. He owns a 2020 T-cat, his first Cat after years of ski-Doos and a few Polaris. Between us we have owned nearly 60 sleds of all brands. He has 50 years of riding under his belt and I have been riding for 45 years. We also have the opportunity to ride all the newer models from all brands as our group we ride with is pretty diversified as far as makes and 2 stroke and 4 stroke.
We both agreed the newest version of the Pro-cross with the 3 cylinder turbo was the very best sled we had ever ridden.
It is , by far, the flattest cornering sled on snow. As a trail sled, balance is very good. Mountain sled? Probably not, but I cant speak to that as I have never ridden one in the hills or ride off trail.
I know it isnt for everybody, but they are VERY good. All it takes to convince some people is a test drive.....an an open mind.