The Pantera's dealer mark-up per car was higher than any other Ford/Lincoln/Mercury vehicle had ever been. The dealers made money on them! Corporate Ford's gross income on the project was over $5M (1970 dollars). I'll bet that exceeded their expenditures too. The sole purpose of the car was to increase foot traffic at Lincoln dealerships, which it did. The project cost Ford nothing, the dealer's profit was unprecedented, and the Pantera succeeded in bringing customers to Lincoln dealerships. Sounds successful to me.
There were insiders at Ford pulling to keep the Pantera alive. Technical & production issues were there, but many had been resolved by 1974. The US market went soft on performance cars, but Ford wasn't manufacturing these cars, DeTomaso automobili was. The pinch of low production numbers is felt at the production end. In other words, DeTomaso felt the pinch, not Ford.
The true issue that killed Ford's involvement with the Pantera project were personality (ego) conflicts. Ford brass wasn't going to tolerate it, so the word came down from the top, pull the plug.
If you want a clue, notice that the US GTS Panteras have no DeTomaso badges on them, not one. The DeTomaso badges were all replaced with GTS or Ghia badges (by 1974 Ford owned Ghia). Even the sales literature was edited and any mention of DeTomaso was removed. It was personality conflicts that killed Ford's involvement with the Pantera.