Again, not sure what you?re picturing.
With a captured spring set up, compressing the spring, pulling the clip, swapping and compressing the new spring while slipping the clip back on takes much more hand strength and manual dexterity than assembling a pistol with an uncaptured spring. I?m not saying swapping springs on a captured system is hard to do, just harder than assembling a pistol with an uncaptured spring, which is nothing.
An uncaptured spring is ?captured? by the slide when you assemble the upper, in the exact same place the captured system is. There?s nowhere for it to go prior to pistol assembly. It?s no less stable than a captured system. It?s the same as with a captured spring. Same thing.