I don't think people were opposed to Ten Hag bringing in players who had previously played for him on principle. The issue was that he was failing to account for whether the players he was bringing were of the required standard, and placing too much emphasis on players he'd worked with in the past.
Nuno Mendes is one of the highest performing left-backs in world football from an attacking perspective, and we are in dire need of an elite attacking left-back. If you were to pick any player on the planet to fill the gap we have at left wing-back right now, I don't think it's an exaggeration to say that Nuno Mendes would be near the top of the list. That'd be true even if Amorim wasn't the coach.