The braking distance grows as the square of speed. And the mass that is braking is of course also a factor.

Again, time. The faster vehicle occupies more road but for a shorter time. That fast car down the road and that closer/slower bicycle both occupy relatively similar amounts of roadway in comparison to multi-person vehicles like busses. The fastest way to move people down a given lane is to cram them into trucks army style and then drive slow enough that each truck leaves minimal time between each. A lane can then handle a 50-person truck every 5 seconds, or 10 people per second. That's far more than can be pushed through on individual bikes riding in pairs.

This is assuming a chink of road in isolation. There's also intersections, vehicle separation, signaling, and other needs that take up less space-time on a bike than a car. Perhaps less-so than a bus, but we would probably need simulations to say more.

Of course, but for a discussion of bottlenecks signalling isnt an issue. Putting an intersection at a bottleneck is just stupid. Thats why bridges fan our thier roads on either side.