Really only some of the pre-war preamps have treble boost EQ because the 44-A drooped up top. Once the 44-B existed they stopped adding more, besides what the transformers add with resonant top boosts. The BA-2 still has the EQ boost, and it's a pre-war product. Many of the transformers show a resonant top boost, and that is true across most manufacturers. That boost does add 'air' to ribbons, it's usually above 14K. There is the occasional RCA amp, usually the dual purpose line amps, that is ruler flat and rolls off steep early, those will easily make a ribbon sound dull compared to the others, but maybe still better than a modern transformerless pre with a fixed sub-2K input Z.

But then, even a Mackie 8 bus preamp is a 5K input Z, so maybe it's better for ribbons? : ) For loading at least, compared to some, but then no 'free' transformer gain at all, with the input transistors doing the hard work.