Is it ethical to withdraw a paper after reviews?
There is nothing to do with ethics as question asks. This is simple professionalism. The journal has devoted enough time for reviewing the manuscript. The reviewers have put in their efforts.

If you are really fixed about not go ahead with submission of revised manuscript, then do the following:


Don't submit the revised manuscript to the journal.
If the journal editor asks about the revision, then say that you are extending the article in various ways and would not submit the manuscript. But, thank them for their efforts.


But, I would suggest that you had made a mistake not looking at the journal statistics, you should go ahead with this journal with the publication.