Not necessarily.

While `"use strict"` came in ES5 and `let`+`const` came later with ES6 what is worth remembering is that `var`, `let` and `const` have different features and that then means different usages. `let` and `const` don't make `var` obsolete, they make it less powerful.

Here are more details about `const`, `let` and `var`:

- `const` is a signal that the identifier won’t be reassigned.

- `let`, is a signal that the variable may be reassigned, such as a counter in a loop, or a value swap in an algorithm. It also signals that the variable will be used only in the block it’s defined in, which is not always the entire containing function. 
- `var` is now the weakest signal available when you define a variable in JavaScript. The variable may or may not be reassigned, and the variable may or may not be used for an entire function, or just for the purpose of a block or loop.

In other words here are differences between these three:
- `var` declarations are globally scoped or function scoped while `let` and `const` are block scoped.
- `var` variables can be updated and re-declared within its scope; `let` variables can be updated but not re-declared; `const` variables can neither be updated nor re-declared.
- They are all hoisted to the top of their scope but while `var` variables are initialized with undefined, `let` and `const` variables are not initialized.
- While `var` and `let` can be declared without being initialized, `const` must be initialized during declaration.

Here are w3schools page explaining "use strict": https://www.w3schools.com/js/js_strict.asp

I hope my explanation was helpful. Cheers!