Beg to take issue with you. The battle scenes between the Enterprise and the Reliant were the idea of Nick Meyer, director of the film. Paramount, or rather Harve Bennett, liked it. But there was no insistance from the studio on a battle scene at all.
When Harve Bennett was first approached by Paramount they asked him his opinion on TMP. He said he thought it was boring. They asked if he thought he could do better. When he said yes, they added "can you do it for less than forty fucking million dollars?" Bennett said he could do six movies with that much money and got the job.
A cheap action movie, that's what Paramount wanted and what they got.