I don't know how you can claim, with a straight face, that winter hiking/climbing is easier than summer. But my experience is mainly in New England and DAKs and the White Mountains.
Days are shorter. Nights are longer. Temperatures far lower. You are surrounded by, and walking in, frozen water. So how can the odds of hypothermia be lower than in summer? This is nonsensical.
The trail is harder to find. Blazes are covered over. The footpath disappears. You're carrying far more weight in traction gear, sleep gear, insulation.
Read the news each winter in New England, there are often one or two hikers who pay the ultimate price for their hubris.