You should chat with the moderators of those groups - I'm positive that they're having a similar experience.

For people that have already been whitelisted in (and assuming that you don't get spoofed) the experience is great. For those running the group? Not so much.

Our list is obviously smaller, but with somewhere around 1000 members, I don't find the moderation duties difficult to keep up with. And we've only let spam through a couple of times.