when I learned to build frames back in the '70s, there wasn't any question about bridges, we put them in. Since then, some of the newer tubing doesn't do all that well with the stress riser imposed by the chainstay bridge. This was a hard lesson learned by many builders who ended up with broken frames. Now I have to convince myself to put a chainstay bridge in because of this issue. I usually do anyway so I can mount fenders. I have thought about just putting a cantilever beam off of one stay for this, maybe I'll do that on the next build.

Leaving off the brake bridge is a little weird, but I don't think it will hurt anything on a bike with a modern tubeset. The bridge does protect a little against bending in a crash, but high strength modern steel tubes are not that likely to bend unless it's a really bad hit. And then it's likely that you only have to replace one stay.