I've never known all weather tyres to be that good.
Jack of all trades but master of none 
The reviews often say that 'all season' tyres are relatively weak on snow

A lot of the youtube reviews don't compare winter and summer tyres. Many of the videos show how much better winter tyres are versus all season tyres on snow AND ice.
Many people say winter tyres are not worth it for the UK climate. Yes, we have had had several years of mild winters. However, I don't remember any recent winter without frost and black ice, in my area. There was 1 recent winter with just 1 weekend of frost. A local garage was full of crashed 4x4s the next week. And the NHS were recently asking for 4x4 drivers

I would not swap the winter tyres on my wife's car for all season tyres. To me, winter tyres are worth the hassle and cost, for the peace of mind knowing my wife's car is as safe as possible in winter.