I've been using Starlight on Master Mode just to see how good it was, and range is definitely a problem. However, having challenged Empress before Martian Madness and the pillars (albeit less-so, since you can just run in and out of the Solar Pillar to get yourself the immensely better Solar Eruption), I can say it has a little bit of use there for tearing down crowds. It's not as range-deprived as other high-speed melee weapons, making it useful for more dense crowds that don't take up a lot of space. Naturally, it wasn't that hard to avoid damage either due to its extra bit of range and the mobility provided for you this late in the game.
Using the Starlight, crowds of Gray Grunts, Martian Walkers, Engineers, and Gigazappers were torn down pretty quickly, whereas other weapons Melee has might take a bit longer and leave you a bit more open.
Hell, I even used the Starlight against the Martian Saucer. The Saucer is definitely a lot slower than previously, and I found it safe to use on the Saucer when it was doing either of its laser-based attacks due to the speed you could get using wings like Steampunk or better. It shredded the Saucer impressively quick. Of course, when Phase 2 came around, it was better to just dash dance and use a weapon with more range.
As for ranking, I'd say your ranking is pretty accurate, but a hidden gem in certain areas. Considering that Fetid Baghnakhs are quite powerful and serve a similar niche but are one tier ranking higher (at B), I'm sure Starlight could stand to be moved up to B- simply because of its sheer power and capability of doing away with hoards you have the capacity to maneuver around, giving you more time to deal with other threats. Just my observation, though.