Weight is not the prime consideration for what role a 'Mech fills. Speed, armor, and weaponry brackets are.
By that measure, the Stooping Hawk is... not a medium, but a heavy cavalry, so it deserves to be compared to 'Mechs like the Gargoyle, Timber Wolf, Summoner, rather than its nominal weight equals - and can't do the quite the same jobs as an Ice Ferret or Stormcrow or Dragonfly.
The Stooping Hawk compares well to those much heavier 'Mechs - unlike the Nova, which is strictly worse. It's almost frightening, actually, and shows how slim the gains can be for poorly designed high-weight, high-speed 'Mechs. I mean, it only loses 5.5 tons of warload (DHS, armor, podspace) compared to a Summoner, and leverages its configurations much more wisely.
Sadly, in Alpha Strike it isn't quite unique, and the aforementioned heavier designs benefit from the greater abstraction, so I have to think, "Do I want to get another heavy cav member for my already-overstuffed heavy cav Star (Timberwolf, Gargoyle, Executioner, Naga, Summoner), or do I pick another high-speed omni to finish off my strike Supernova? Hello, Stormcrow, you are really, REALLY good even here... and Ice Ferret, you come in at a strange cutoff for armor conversion that suited you quite nicely..."