> If a component is memoized with `memo(...)`, then a re-render will be stopped if it has the same props as before

This works only with immutable data structures. Am I wrong? Because a modified array will pass the identity test (=== operator). If you are using mutable data structures, you cannot use identity operator to detect changes.

Also if "memo" optimization is that good why does one have to add it manually?

> If your react app is re-calculating the entire tree, you suck at react

The point of UI framework is to do the optimization for me and not require me to use some special style of coding like immutable structures or manually write functions like componentShouldUpdate. What I write is how UI variables depend on model variables and the rest is framework's job. I don't want to use weird patterns like a function with a giant switch that processes update events and clones the whole model graph to change a single variable.

Vue of course has its own set of issues, caused by using proxies (for example when adding on object to the set you must "unwrap" it manually to prevent adding a proxy to the set).