I wouldn’t, but you’re not much of a product designer if you can’t get your ideas across using simple tools like a sketch on a whiteboard (there was|is an app the let you take photos and link them using active areas).

So you can take bootstrap (or even raw html) and create something useful. Then you make it nice, not the other way around.

You would have to be a big outlier to feel the need to create a custom widget. Most widgets have been defined since decades.

I agree that design is about primitives. wireframes and IA should come across clearly at any fidelity.

But i don't think that's what tailwind and bootstrap are doing. But people very much use these tools to "solve design".

The layouts, widgets, and primitives in these tools are not primitives. I can't deny they get tons of people very far very fast. But my main disagreement is that all of this isn't design and it's not what designers do. You touched on what i agree with: UX flows, diagrams, stories, journeys, personas, etc, these all need to be designed and connected in reality using various primitives for the medium.

Then you slap a cohesive paint job on it, interaction elements, tone and terminology and yes, there is that element of design too.