That is some super blunt advice from Nana Visitor’s manager, and we’re lucky she ended up not taking it.
TV in general was still largely looked at as a jumping off point for eventually getting to work in movies, so the idea of potentially having a long-running career playing a TV alien (especially) was seen as something that would only end up hurting Visitor’s chances of moving away from that type of work down the line.
Her manager, obviously, thought that DS9 would have her pigeonholed.