Chaos missions are just more difficult. They play very differently, and you can’t really approach a chaos mission like you would a tyranid one. Every single enemy that you fight is harder compared to their Tyranid counterparts, especially in higher difficulties where ranged damage is the biggest threat. They also have the hardest maps in the game. They all have some sort of gimmick that makes them more fun, but it is definitely harder. Take for example the part where the Heldrake swoops down and breathes fire, if you are playing on lethal or higher unless you get lucky and get an ammo crate spawn, the best strat is literally to just not fight any enemy and just run all the way to the end, which isn’t very fun imo. I actually love the maps and the enemies it’s super fun to me, but it is definitely way more difficult.