Thats a yes and a no. Budgets can go over, the studio heads don't know how a film will turn out beforehand. When they greenlighted Tarzan, Pan hadn't bombed yet, and all of
Snow White and Huntsman, Maleficent, Cinderella, Oz, etc..
Had been pretty big hits.
They also had a safe director from two highly acclaimed Potter films at the helm. Sure, the movie didn't work out like they had initially planned, but that isn't going to always happen.
I doubt the initial budget was so high, and I doubt they planned on the movie turning out like it did quality wise. By the time things weren't turning out how they planned it was likely too late and so they probably decided to eat the costs and go light on marketing.
Studioheads can make stupid decisions, and then sometimes something can seem completely safe and it turns out wrong.