I will say this, and I mentioned this before, I happen to like the Topeak Tourguide DX, while it isn't waterproof but you can do some things to prevent water from coming in. When I say waterproof in a drizzle it's fine, but in a downpour it's not, so what I did was to sprayed Kiwi Camp Dry Heavy Duty water-resistant spray, I put on 4 coats initially allowing each coat to dry between coats, then I redo it every season. The bag also comes with a rain fly which I also put 4 coats on it and I retreat it every season. Even after all of that anything that I don't want to get wet I put in ziplock bags just as a precaution. I have waterproof panniers, and those were also tested in a downpouring rain and nothing was remotely even damp yet I still put stuff I don't want wet in plastic ziplock bag, But I also use a heavy-duty garden trash bag to line my panniers mostly to keep anything that spills inside from staining or stinking up the inside of the bag, but it will also assure no water gets in. One could line the handlebar bag with a smaller trash bag and waterproof it that way, I have not done that.
This Topeak bag is significantly larger than Ortlieb, plus the Topeak has a large clear plastic cover for maps that the Ortlieb does not have. So while the Ortlieb is better at keeping water out you can make the Topeak do the same thing for cheap.