I’ve led 3 horses at once, with 12’ leads, without any problems. I don’t have issues not being able to manage that length at all. In fact, it makes it a lot easier because the outside horse on one side has enough line to not be walking on top of the inside horse.
The length is easily managed with a double back loop (not a circular loop, ever)
Even a 5’ long rope has to be gathered somehow - how are you doing that? If you’re holding it 4’ down, that’s a lot of room for a horse to jump around. If you’re holding it right under the halter, that’s a lot of rope swinging that could wrap around a limb if the horse jumps around
My 12’ line has a leather popper at the end. It makes quick work of dealing with some unexpected spookiness, without having a heavy knot at the end to have momentum that’s harder to stop. Granted, that knot is useful to hang on if you get to the end of the line, BUT, at least IME, that happens far, far less often when there’s extra feet of line to get the hind end pointed away from you to stop a bolt.
And finally, it makes it very easy to do quick ground work sessions without having to swap from a “leading line” to a “working line”. I can do in-hand work and use the last few feet in one hand as my “whip” to do some directing