Pompous Battlemage // Improvised Act was first printed on 10/2 in Reality Fracture. Only 25 Prowess entries are in the data for the week, and the "with" group has just 19 matches.
One or two events could swing these numbers a lot. Treat the gap (about 24 points) as an early signal, not a firm conclusion.
The winrates use each entry's recorded wins and losses. Draws are excluded, and there were none in either group.
The same query would show whether the Battlemage decks differ in other ways, such as the builds or the players. I haven't run it.
Sources
Data from 10 tournaments in the window: 90% MTGO, 10% Melee.