The virtual DOM is not faster than performing direct mutations of the actual DOM, the virtual DOM is a tool that allows the normally slow approach of "blow away and rebuild the world" to be fast enough to put into use.
Prior to React, performant apps that weren't using frameworks that regenerated the entire DOM tree would simply manually mutate the DOM nodes based on what it was doing. If your app was loading a new comment, it would find the list of comment nodes and append a new one to it, same as a virtual DOM would.
The problem is that this could be error-prone in large apps—are you even sure that the comment list is still on the page? If it's not, do you need to add it to the page or is this a completely new view and you're reacting to a network request that finished after the user navigated away from the page? That's the kind of finnicky manual work that React helped simplify, but the performance was the same as an app manually mutating the DOM plus the extra virtual DOM comparisons.
https://www.quirksmode.org/dom/innerhtml.html
https://segdeha.com/experiments/innerhtml/
The thing which was slow is changing more than you need to change. When the React marketing push included performance, that’s almost always what they were comparing it to - someone would have slow code making the same updates multiple times or triggering reflows by forcing the browser to do a partial update to measure something, and then updating again.
There’s an argument that the guaranteed overhead of using React is better because it helps the average developer who doesn’t measure performance much do a better job than they might have otherwise, and that can be true for many people but it also tended to get oversimplified to “React is fast” despite widespread evidence to the contrary.
But in a comment thread of people saying the virtual DOM is not faster than equivalent manual DOM mutations you can understand why "The virtual DOM was faster than the DOM" got understood differently since it lacked that clarification.