I am not saying either way - that they were or were not, but I am just curious how you determined your view?
This is one of the perennial problems with any additive - the ability to objectively verify their benefit/waste.
I have over the years heard good things about Marvel Mystery and use it to do some special oiling (guns, etc.) and have heard good things about it when used both as a gasoline additive and as an oil additive in the crankcase. I think one of its great advantages is that it is highly detergent which loosens deposits here and there - esp. in hydraulic lifters.