Have you scrutinised the negative with a 4 to 8x loupé, or passed judgement on the sharpness by some other means e.g. holding neg up to light? A finished drum scan will give an overall impression on the definition of a lens and film, but all that is useless if an average lens, poor technique and even poorer scanning conspire to derail assessment.

I used an orange filter in my student days with Plus-X almost three decades ago and cannot recall any sharpness derangement issues from what was printed and exhibited in those days, even with the rather lowly standard of filters available way-back-when. Today we are fortunate to have so many exceptionally high quality filters available. B+W filters will not introduce a lack of sharpness, but resin filters will, and I have never stooped to use those things with any highly corrected lens. With all filters there is an increased risk of flare (exceptionally well controlled with today's multicoated filters) and, where more than one is in use (not recommended), ghosting and a loss of contrast. You could of course keep shooting without an orange filter e.g. try a red filter.