Is the business of improving a thesis a continuous process?
This is essentially a question about the nature of the writing process. There is not a single true or false answer, as people have a variety of different writing processes. A certain percentage of the population, including many professional journalists accustomed to writing on tight deadlines, are what compositionists refer to as "first final draft" writers; in other words, they write essays with little in the way of revision. Other writers tend to revise extensively in the process of drafting an essay.
One method of writing a research papers involves doing extended research and then writing the complete essay with minimal revisions while another method is more iterative, involving developing a preliminary thesis, doing research, and then revising or refining that thesis. No one method is inherently better than another, but different methods work well for different writers.
As you progress through your university career, you should try different types of writing process until you discover the one that works best for you.