No it isn’t. I upgraded my copy to use PHP 7 as soon as PHP 7 was available even though it wasn’t for a couple more weeks before XAMPP offered a version that included it.
I also upgraded it to mySQL 5.7 rather than switching to mariaDB.
While it is easier to install all the products included in XAMPP in one go using the package than installing each separately, it is actually easier to upgrade each product separately than it is to install a replacement version of the entire package.