Comparisons

"The virtual DOM is fast" is the claim, and it is not a claim at all until you name what it is faster than and at what. It is faster than naively rebuilding the DOM by hand on every state change, because DOM mutation and the layout it triggers are the expensive part and diffing avoids most of it. It is not faster than not diffing — a fine-grained system that knows which text node changed does strictly less work than one that re-runs a component and compares two trees to find out. What the virtual DOM buys is a programming model: render as a pure function, no subscription bookkeeping, and no rules about how you may read a value. The costs are real on both sides. The diffing model spends main-thread time proportional to the re-rendered subtree, which is why memoization and keys exist and why an unmemoized provider can re-render half an app. The fine-grained model has almost no diff cost but the reactivity is *where you read the value*, so destructuring a value out of its tracking context silently breaks updates, and dependency graphs can be harder to debug. Neither is the winner; they fail differently, and the failures land on different people.