In 1972 just about all of us carried our extra ammo in cartridge loops. When reloading I practiced withdrawing and loading 2 rounds at a time, thinking that would cut down reloading time.
About 1975 we started seeing the Bianchi Speed Strips, which became very popular very quickly. As others have pointed out, selection of a pouch that would accept the Speed Strip was critical (not all would do so). Also, after long use the cartridge pouches could begin to collapse, losing their original shape, and this could make it difficult to withdraw the loaded Speed Strip.
Shortly after that HKS introduced their speedloaders, in virtually the same design as still seen today (a testament to an excellent design). Safariland followed with their own speedloader design, also very good. For either type carry pouches can be an issue, all being somewhat bulky on the belt, and some not allowing an easy and solid grip on the loader as it is withdrawn.
Throughout the 70's and 80's I've seen many different problems associated with reloading revolvers quickly under stress. On the range, during timed events requiring reloading, I've seen ammo scattered around on the ground and guys scrambling around trying to pick the loaded rounds out of all the spent brass. Tabs torn off the Bianchi Speed Strips were very common, and after some use the rubber around the cartridge rims could tear away. Grabbing a speedloader out of the pouch by the release knob can cause inadvertent release of the cartridges leaving the shooter with an empty speedloader in one hand and empty revolver in another hand. Dump pouches dropping 6 rounds into the hand for reloading seems like a good idea until you have to fumble with them under stress, frequently having to pick up several off the ground.
Interesting story about an old timer I knew back in those days. On the range or on the street he never used cartridge carriers. He carried his ammo loose in a pocket, reloading one round at a time as needed. His range routine was to eject his empties and put those in another pocket, saving the need to police up his brass after the end of the course. One night he was involved in a gun fight with a couple of bad guys barricaded behind a car, after which he found 12 fired cases in one pocket, where he had put them while reloading his revolver twice.