The invisible mobs are the ones that are already there when you first load in. It looks like the friendly NPCs are punching nothing / thin air. The ones that run in afterwards are always visible (for me, at least).
I don't understand how CC helps here. It's Group Finder, so I end up with groups like PT (tank), Sorc (heals), Sniper, Marauder. That lets us CC... one mob. Out of like 20 mobs (or 12, whatever, it feels like an infinite army).
I understand you can do fancy coordinated stuff like Flashbang chained with Roar but I have to be honest, that's expecting too much from Group Finder. Most people will just rush you, charge in for you, or break fragile area CC instantly if it isn't marked. Plus, even in a best-case scenario that only buys a few extra GCDs. That seems like too tight a margin for Group Finder content.
And the friendly NPCs:
- lose aggro immediately if you hit any mob once
- don't gain it back
- do barely any damage
So they could just as well not be there and I don't think there would be any difference once you engage.
I appreciate your suggestions, I just don't see how that stuff would really help the situation. I feel like I'm missing something, like you're not actually intended to fight a giant swarm of Strongs like that and I'm doing something wrong. But I can't figure out how to prevent it.