He struggled badly in his few cameos early last season, totally understandable given his age and injuries, but then hit the ground running in the championship. Maybe he developed a lot in his last month or two with us but his sudden burst of form seems down to how poor the championship is as much as anything.
While we don't have any backups that can touch the quality of the starting three, Origi is a proven scorer with a ton of pace and power, Shaqiri is a proven scorer who interplays well with the rest of the team and Minamino uses the ball well and presses well but has some issues with the physical side. For Brewster to force his way into consideration he'll need to show a bit of everything in my opinion, he'll need to press, score goals, pass well and show a good amount of pace and physicality.
Given there are some truly poor strikers in the PL the ideal situation would be for him to go on loan to a lower level club, unfortunately most will be fighting for survival and aren't likely to give him a ton of minutes over more experienced options, he's in that awkward spot now where a championship loan will only help so much and he probably isn't good enough to be a core player for us yet.