These "very new things" have, in part, been available for more than 6 years now. Not to speak of all the other PHP features WordPress chose to forgo, like PDO with prepared statements (which completely eliminates SQL injections), which came out 21 freakin' years ago.

There are many very successful and professional PHP projects with millions of users that seem to be able to migrate to newer PHP versions just fine.

Whatever the WordPress developers are claiming are the reasons for their irresponsible codebase and their inability to improve it is nobody's fault but their own.