Managed to clear Castrum on 5 people, but not on 8.
First, let me say that I hate bozja with the sort of burning passion normally reserved for only the most heinous of crimes. If the place could be razed to the ground I would open a champaign bottle on the crater.
Second, I've previously managed to clear this cursed place on 5 people, just allocating 2 Tanks on bottom and 2DPS on top with a Healer, we did perfectly fine, managed to protect the Tunnel Armor marginally well but the boss died before it became an issue.
And I have failed on 3 people before while trying to solo bot and leaving the other 2 top, we failed because there wasn't enough bodies to soak the Tunnel Armor. So I've come to the conclusion that 5 people would be sort of like the bottom cap and it just becomes insultingly impossible under that.
But now I've FAILED with 8 people, because we organized 3 down bot, 2 Tanks and a Healer, while everyone else went top. We failed to kill the Helldiver before the Tunnel Armor got destroyed. Then we were doing fine going an even 4-4 split and we ran out of time.
What's my point? I've got no point. I mean, maybe "I hate Bozja" is a point? Sure, let's go with that. I hate this cursed place and I would happily drop another meteor on it. Twice.