It is a feature if it works, but whenever the text the text fails to reflow correctly, or an attempt to zoom into a figure causes the entire page to reorganise

It is a feature if it works, but whenever the text the text fails to reflow correctly, or an attempt to zoom into a figure causes the entire page to reorganise itself and (worst case) replace the figure, then it really annoying. The fact that reader mode is often the best way to read websites on mobile suggests that either HTML has got this feature badly wrong or has provided features that are being very badly used. In comparison the fairly common two column format of scientific papers is quite readable on my phone after zooming into a column.