Most definitely, in my opinion. As stated here: https://symfony.com/doc/current/templating/PHP.html
Deprecated since version 4.3:The integration of the Templating component in FrameworkBundle has been deprecated since version 4.3 and will be removed in 5.0. PHP templates will no longer be supported and you’ll need to use Twig instead.
Since Pimcore in its current form relies on Symfony (it IS a Symfony-based application, after all), unless they move away from the framework (which I doubt, since I bet the transition from Zend has been painful, to say the least, and Symfony has a HUGE community), they will be forced to abandon PHP templating in future releases completely.
Regarding Symfonys policy of such a move, I think it’s completely understandable, since Twig is easier to develop in (for front-end devs at least). And you get an added bonus of completely removing the backend logic from frontend, since all the relevant code remains in the controller. With a PHP template, inexperienced devs easily fall into the trap of making backend changes in the template which should never be the case.