I agree that rubber compounds are better now, and actual condition may be more relevant than an arbitrary age. Especially if summer and winter tyres are swopped and spend much of their life stored out of harmful sunlight.
But they may still suffer from microcracking and deterioration , as can the rubber used in tyre valves.
But do I have the skill to spot serious degradation ? I would rather not find I was wrong by a high speed blow out.
I think 1.6mm is pushing your luck. Far more likely to aquaplane in the wet. 2mm is better.
I'm skeptical about Michelins claims, albeit lower tread Michelins may still be better than other brands with more tread depth. Sounds like a marketing strategy.