I theory crafted a pretty cool combo with a tyrant champion FA. They've already got great defenses, so that makes your swarm very tough. If they attack you, they have to take damage or go prone, if they attack the swarm with a strike, they do reduced physical damage which is a loss.
Also if they're prone and they get immobilized by webbing, they're stuck now!
And while it is really slow, you could almost lean into that and once you get Carried With The Swarm you can double down on ac with a fortress shield and let them move you.
It's also really cool if you can pick up the swarm domain for flavor, really makes you the king of swarms.