According to official Google statements, RankBrain does change rankings, although it’s not a ranking factor per se.

Rankbrain has the ability to change rankings by re-calibrating the importance of other rankings factors, depending on the query, geo-location, browser language, and, to a smaller degree, user search history.

“It [Rankbrain] does change ranking, e.g we’re better at getting relevant results for negative queries” – source

@randfish I meant any ranking component. It does change ranking, e.g we're better at getting relevant results for negative queries

— Gary "鯨理／경리" Illyes (@methode) March 18, 2016