It does lower speeds, you can’t just fly through a roundabout even if you’re going straight through. You can easily blast through a regular intersection at 100mph if you want.

They have higher throughput though, so it’s “faster” in that sense. Lower peak speeds, higher average speeds (as you’re not stopped for a long time).

That's the point of a roundabout. It lowers speed at the crossing while also increasing throughput compared to a regular crossing.

So you can indeed lower speed at a crossing area while not lowering the speed of traffic overall, just by eliminating the waiting times.

don’t need to dramatically lower speeds

They lower speeds, just not to a stop which is good for traffic throughput and emissions.

Alex, what is a "pedestrian bridge" for $500?

In roundabouts you only need to look in one direction of incoming cars. In a regular 4-way intersection you have to look in three directions. Your comment makes no sense to me.

You mainly need to be looking right (flipped for anyone who doesn't drive on the left) pretty much all the roundabouts here that regularly have pedestrians will have triggered traffic lights or the pedestrian crossing at least a car length before the roundabout starts so if you're entering a roundabout you're almost always in front of where people will cross if they're not just being dumb. Once you're used to roundabouts they're pretty formulaic and the biggest problem (for me anyway) on an unfamiliar roundabout is knowing which lane to be in, not the traffic already on the roundabout.