What do you think about creating a substitute for PostMan? As a dev it's one of the tools I use the most every day and also loathe the most yet there's no good alternative.
Value proposition:
Easy sync & sharing with the whole dev team (dynamic and interactive documentation).
Quick opening and lightweight on any platform.
Simpler and better UX, easily customizable requests.
I'm not a very heavy Postman user, so I can't really give you feedback on the first point.
For the other two points though, I've noticed that providing a better UI/UX & loading speed is important to make users stick around if they're interested, but it's not necessarily going to convince them to switch to a different software or start an onboarding.