The user does care. At a previous company we started migrating from angular to vue. Vue was so fast that those parts would be completely rendered and the rest would be white. It was also snappy.

Of course, one has to be mindful about the transition. You cannot stop business, but you can take a little extra time whenever there's need to modify a section to improve quality (both code and ui). Actually that's why we chose vue, it allowed to a progressive migration out of angular.

BTW, someone had the "great" idea of not using a framework for an internal admin portal. It turned immediately into a huge ball of mud.