Gradual growth =/= many tacked on features. Many tacked on features =/= technical debt. Technical debt =/= "everybody is afraid and frozen." Those are merely often correlated, but not required.

Whatsapp is a terrible example because it's barely a product; Whatsapp is mostly a free offering of goodwill riding on the back of actual products like Facebook Ads. A great example would be a product like Salesforce, SAP, or Microsoft Dynamics. Those products are forced to grow and change and adapt and scale, to massive numbers doing tons of work, all while being actual products and being software systems. I think such products act as stark rebukes of what you've described.