The article doesn't go into details whether these academics are full professors or e.g. postdocs. Twenty-five tenured professors would be a big deal because they tend to either bring their workgroups along or rebuild them at the new university. That's where the true impact of such news lies if these are indeed teachers: these groups produce a steady stream of future experts in the form of graduates and PhDs in their respective domains. Given the timelines for careers of students and young academics, the full impact of these moves should start to show in about 5 to 10 years.

Another factor is if they're all from the same (sub)discipline. It doesn't take a lot of established researchers moving to shift a field's center of gravity somewhere else. When you start seeing research conferences that used to be in the US be held elsewhere instead, you'll know that the change has happened.