In the "other" train magazine, the one from March 1993 with Neil Young on the cover, there was a very interesting article, often overlooked, called "Scale's the thing." In that article, the authors came up with a four tier grading: Small being 85% or less of scale, Medium being 85% to 93% of scale, Large being 93% to 100% of scale, and True O being full scale.
According to this article, there were postwar locomotives that were scale in their overall body proportions, but obviously not in either detail or the mounting of trucks to the body. Or the stamped sheet metal handrails.
The postwar GP9, NW2 and Train Master are all listed as scale in the article. The F3 is listed as large. The K-Line S-2 is listed as medium, as are the K-Line and Lionel Alco FA diesels. Steam engines are really all over the place, then as they are today. The 2-4-2 and 4-4-2 Columbia/Atlantic starter set steamers are small. The Lionel 773 Hudson is listed as scale. Of course, some of this really comes as no surprise to any of us who have been in the hobby for some time. Still it is an interesting article if you happen to have that issue of CTT.
Yet by current standards, most folks modeling a scale 3-rail layout today probably wouldn't consider these postwar developed engines for their layouts. These products, having been developed before the real push towards scale products beginning in the mid 1990's, have now fallen under the banner of traditional products. Most of the so-called traditional line products have less fine details, more rugged construction and compromises to allow them to navigate tighter 027 or 031 curves and turnouts. We often forget today that Lionel of the postwar years had their categories of "027" and "0 Gauge" in their catalogs in lieu of "traditional" and "scale."
Yet as @raising4daughters alluded to, some of the traditional line products (as the tooling gets refurbished or recreated) have better detailing today and certainly better decoration and paint.
