Agree that conventions are subjective and do change.
But I don't think tools like Webflow are just starting points and to be eventually discarded. I seen many makers stick with using these tools even when they can code. In the end it's a preference and subjective, like you mentioned earlier.
Many devs think visual tools are just for beginners, like training wheels for kids' bicycles. I think there's a group who continue to enjoy using it and want to keep using it out of intention and choice.
I agree with your last paragraph — which was the intent of my last two paragraphs, which I think you misunderstood.
… The tools are good starting points for learning and for designing “simple” projects for which the design tools are intended.
As the project grows in complexity, the tools are inevitably discarded.…
The “discarding” is inevitably caused to the tool’s inability to meet the complexity of a project. Not because the tool is viewed as a “toy”.
Those tools are always useful for creating initial designs. And as design tools or any IDEs, they have their own limitations that one has to be mindful of.
Yes, it's only logical to switch if it no longer fulfils its purpose.