While I consider a “Bossing SMG” to be almost an oxymoron, I do get good results out of the Fatale against bosses that aren’t immune to Cryo. Overall, you’re probably right though.
That’s the challenge with Nisha IMO: you sorta need a diverse loadout to deal with ammo shortage but most of her COMs are pretty specific about what they boost. That’s what makes a CoE build good for mobbing (Too bad you have to switch out for bosses). That’s also why the Crapshooter is so versatile. (And why I love the Sheriff too)
It does sort of spell doom for the Cowgirl, Rustler, Kid and Desperado, even though they would be interesting otherwise.
Her non-elemental skills help in that regard as these guns work against everything so you can diversify your loadout while still having most guns be good against everything.
You’ll notice that pretty much everything in the TG is picked because they milk the most out of every ammo spent.
I did a small analysis on this long ago
Fan the Hammer: an analysis of a broken playstyle