I agree with you on that. But it's not a terrible idea to temporarily switch to a 0w20 when 5w-30 is spec in extreme colds where you don't have access to a block heater and don't do long drives since the oil will never thin out. But by extreme colds i mean like 25 below zero or worse. If it's just 15 below I wouldn't think twice about running a 30 grade year round.
I prefer to only use 5W-30 in all my vehicles, as the higher HTHS will protect better during high heat/high RPM driving like going up extended inclines with 8 people + heavy luggage in the vehicle and air conditioning on. To the OP, if you haven't already, please google HTHS wear graph.