It hasn't been my experience that coated Rolleiflex lenses [i.e. Zeiss lenses] are radically different in contrast from more modern multi-coated SLR lenses. Mine is a 3.5E with Planar, and I've compared the results to Leica-R lenses [50mm Summicron], Pentax K-mount lenses [various multi-coated fast 50s], and the modern Zeiss lenses for the Contax G. The Rollei has fractionally lower contrast, which manifests itself in a smoother [and to my eyes more pleasant] rendering of tones, but the differences are marginal. I'd expect, most of the time, Rolleiflex images to look better (again to my eyes) than anything shot with a 35mm slr, even one with excellent lenses, just because it doesn't give much away in terms of lens quality, and gains a lot through the larger film format.
If it was me I'd look again at exposure. A hood will make a difference, though. The front element of a Rollei lens is quite exposed.