stainless has ~10x the thermal conductivity of borosilicate glass
Glass has double the heat capacity, and I would assume greater mass due to thicker construction. So unless you are preheating fully to boiling temps first every time, there will be more heat loss to the glass over the course of ~1-3 minutes
Which was my point - 400g of room temperature ceramic is going to absorb way more heat from 250ml of boiling water than would be lost from the glass-air (or even steel-air) interface during the 2 minutes it takes to do a pourover.
If both cones are preheated thoroughly, yes, the steel cone will shed heat faster, however I feel like this is also negligible compared to evaporative heat loss and subsequent transfer to a cup