1. Oxygen cutting is a chemical reaction; the speed at which you can cut is not directly proportional to metalthickness. If you can cut steel 10-20 mm thick at a speed of 375 mm per minute, you can probably cut 50 mm steelat a rate of about 125 mm per minute.
https://www.esabna.com/euweb/oxy_handbook/589oxy21_18.htm
Guessing the lighter sections to be in the 10mm thickness area. 375mm ~15 inches... Aproxmaitatly a two-foot diameter hole for one at a time. that would be 75 inches circumference...FIVE MINUTES???
That said, the vertical elements could be tubes filled with concrete, that would slow the cutting to a near stop for a torch, but not an abrasive saw...
Also, I would expect gaps to minimize wind loading.
We were in the construction business. You usually need water to cut through concrete - so if the tubes were filled with concrete it would definitely be more difficult.