In DMZ, it still has an IP from private range, ergo, still treated as internal -- it doesn't matter whether it is in the same subnet as your users, only whether it falls into the range that the browser considers private.
Maybe our understanding of DMZ is different, for me it's not necessarily with an internal IP - so to clarify, what I meant was hosting it on-premise, but only accessible via it's public IP (as the service is public anyway), which shouldn't be slower if your physical route isn't any longer.
So it doesn't solve anything here.