It's difficult for servers to know how big client allocations are. With v4, pretty much everybody got /32s, but with v6, sizes vary. So you've got to start with small bans, and then switch to big bans later, but not too aggressively so you don't accidentally ban legitimate customers. It's a tricky balance.
You have to do that with range bans in v4 too, since you have no idea how big the pool of addresses a user can pull from is -- and with CGNAT in the picture you're kind of doomed to banning legitimate customers on v4 no matter what you do.
Yes, you ban some legitimate customers with v4. But the span between the smallest allocations and biggest allocations is much smaller, so simple strategies (like banning the bad address) scale further.