That doesn't work if your field is super weird and niche. You end up giving the same elevator pitch over, and over, and over... I suppose it's a "nice problem to have".
I'd be very curious to hear an example that couldn't be summarized as "I am a <blank> doing <blank>".
Of people I know, the most niche I can think of is doing work with programming mitochondrial DNA and my answer for her job would simply be "I'm a scientist studying cells for <insert-medical-company>."
Being able to summarize is one thing, conveying any information is another. There are definitely jobs where giving even a remote sense of what you do takes more than a pithy statement. People either come up with a technically correct bromide like you suggest or some silly pithy "I help teams collaborate better" thing that sounds silly. Unless you're like a doctor or a fireman, it's not so easy to convey real information.
Here's the stumbling block - people aren't looking for "real information" when they ask what you do at a party, they're just looking to get a rough idea of who you are so they can find common ground to continue the conversation.
