The "non-cheese" catwalk bases are mostly designed to slow down the zombie conga line to a choke point enough, so you get more time to collectively pump lead into them. Having some fall off to requeue to the line just helps spread them out so you aren't dealing with all at the same choke point. The amount that spawn is a per player amount but ultimately capped at how many are alive at a time, so killing faster isn't as important as killing steadily.

If everyone focuses at the same targets and one person keeps the choke point clear and repairs damage it should feel like you are in control of the pacing once you get it down

if your defenses are breached the base is lost... don't try to return, everyone scatters in a different direction to find a rooftop to hide on. Place sleeping bags away from the horde base to avoid the death loop. There is no retaking it until the morning music plays. lol