All great points. One area that amuses me though the concern of stroller failure (or strap failure) in a severe crash. I can tell you that if the bus rolled, hit a fixed obstacle, or hit another large vehicle head on (the type of sudden crash with such a deceleration that would "break" one of those straps, or a metal stroller axle....that anyone in the seats (or standing) would be thrown forward. The lack of seat belts would cause immense injury (if not death in some cases). Also, those straps are probably rated for 1000-2000lbs (if not higher), since they have to hold down motorized scooters, which weigh in some cases 5-10x the amount that a stroller does. Multiply by a few Gs, and those straps are designed for that.
While I totally get the crowded concern with open strollers, the idea that an infant is "safer" being held by a parent in the event of a severe crash, vs strapped into a 5-point harness in a stroller, I don't think is quite accurate. The reality is a parent in a sudden accident might involuntarily let go of the infant due to the deceleration forces at play (and potentially being hit by another person or hitting a bar). Also, a stroller weighs less than a human....in a severe crash, a 150-300lbs person will cause more injury to another person than a 30-100 lbs stroller (again multiply the weight be the deceleration Gs).
But again, if you take out the accident concern, plenty of valid concerns about a reduction in space for other passengers.