We are in the process of optimizing GET /rest/api/2/search so that it returns the highest achievable number of entries per page based on the fields requested.
The first optimization is for the and fields. Requests for only these fields enable a maximum of 1000 entries to be returned. Note, however, that this maximum is subject to change as we monitor the live performance.
As with any maximum limit on the number of items returned to a page, we recommended you don’t make any assumptions about that limit when coding.