Can you explain why color film would be a tradeoff against fast lenses? Can't you use the exact same lens with color or B&W? Or what you mean by "traded film for color"? After all, color film existed decades before digital.
I don't know. I only observe the quality fall off when color arrives. Worse, I am not even sure. that my mom's 35mm camera (Canon AE-1) in the 70's shot as good and crisp photos as the B&W cameras in the family in the 40's (before she was born though).
The larger the film stock, the easier it is to get a certain final resolution. Both because the film itself needs to be magnified less when creating the final print and because the lenses don’t need to create as small of an image.
And BW film even today is still MUCH sharper, even if just perceptually, than color film.
...of course many photographers have wept because a photograph wasn't sharp.
Maybe perceptually - due to stronger contrast and perhaps also the fact that B&W film often comes in higher speeds and probably incurs less motion blur of the subject overall.
But I don't think it's actually objectively sharper per se?
The most common frame size used in 120 is a 6x6cm square, especially in consumer cameras of the time. 6x6 cameras stayed popular for snapshots because they could be contact printed straight from the negative, without an enlarger. A whole roll of 120 can be contact printed onto a single sheet of paper and then cut. Much cheaper and faster than enlarging 35mm negatives.
With film there’s no such thing as a b&w specific camera. The difference you’re seeing is probably down to the glass in whatever cheap & cheerful 6x6 rangefinder they took those 1950s family snaps on, vs the photos from the AE-1 which is an all time great camera & lens system.
Slide film is great though if the scene was appropriately lit. Better colors than digital even today. All the catalog photography from the late 90s was medium format slide film and you could blow it up billboard size it had so much fidelity.
Color film typically benefits from optical coatings on the lenses and coated lenses are common from about 1950 onward and uncommon before WWII.