They used to be, they filled an unmet need in the design tools space (clickable prototypes) for years. Lately tools for interface design (Figma, Framer X, Quartz Composer, Origami, etc) have Invision’s main feature baked into their software (where the work is being created) so there‘s less need for designers to use it. Invision intended to get into the creation tools market, but suffered a poorly-managed rollout of their application, and has been floundering since.
This reminds me of Bret Victor’s Bookcase which displays the sections “highlighted” by projecting them on a wall and navigating to that page on an iPad.