no myth but facts
The following is from somebody who knows what he is talking about!
As for the thermal conductivity, aluminium is far better than steel as heat is coming out very easy, so the heat don't stay on the battery, so its life is extended.
As for the electrical conductivity. Its well known that steel is one of the worst metals to electrical conductivity. The corrosion of aluminium is because it is a much more "active" metal to electricity then steel so therefore it needs cleaning. Also we never use steel where good electrical conductivity is required because we loose large amounts of energy. There is not one wire in the world made from stainless steel. We need at least 3 mm wire of stainless steel to reach the connectivity compared to 1mm aluminium wire. Also electrons runs much better on the aluminium that on steel. And if you search though internet you will see that everybody says that steel is a bad conductor of electricity and nobody uses it for that purpose.
The total resistance of a mod is the resistance of its weakest point. So if a mod is made all from silver and only one piece is made from another material then the total resistance of the mod is the resistance of the other material.
You can see in this video too how steel affects the connections:
Electrical Resistance of Stainless Steel - LiveVideo.com
Besides all the above: aluminium is 3 times lighter and of course can be polished way more easily than steel.
So it is clear: Steel has no advantages at all, only disadvantages