Fully agreed on this one, my group has been fortunate to be able to do them via exploits or simply stalling a run just to get them done.
So many of them are incredibly anti-teamwork it is not even funny. The Long Bomb and the Sniper Challenge for the Veteran and Zealot for example require you to have people that don’t immediately take them out, or you just need to have incredible luck on your side.
The Zealot’s Heresy one literally requires you to wipe the team before the 10 minute mark as finishing a run in less than that is actually impossible from what I have seen considering the sheer amount of time-gated events that take place during missions that force you to go longer than that even on lower difficulties. So far our record for a run was on Assassination on the Enforcer Station with 14-16 minutes or something like that on Malice.
Psyker needs to stall the mission for a solid decade to kill the boss enemy with just Brain Burst for how little damage it deals, which of course is a problem as the rest of the team has to now deal with the endless tide of hordes and elites that are going for them and the Psyker while actively avoiding attacking the boss. Not to mention you need to actually explode in order to complete the other challenge.
They really should be designed to be supportive to the experience, not go against the grain. Long Bomb for example could very easily be made to be the same as the Sniper one in that you need to just kill X number of enemies with a single grenade, the Sniper one instead could be that you stun X number of Specials with it at once. How I would design the cosmetic, and progression penances as you could easily call them, would end up being tutorial for the class of sorts.
Those two penances are a good example. People should be taught how their class works in ways that maybe aren’t outright obvious. Another example for the Sniper one as an alternative would be to revive a player while they are within the stun grenade’s radius to show that it is a good way of helping people get up. Psyker’s push could be turned from regular enemies to push an elite off a ledge, the Hound one possibly could be changed to Brain Burst something distant or pop an elite while out of line of sight (if the engine can register that part), things like that.
There should be two kinds of penances in my eyes, actual challenges that should be general like we already have, such as killing 10 Reapers in melee, but the class challenges should be incentives to push you to learn your class so that you can support your team, not actively grief and hinder them just to unlock cosmetics. Again, the core of them in my eyes should be that they can be easily achieved if you play your class with your team, reward the player for being willing to figure out various was that might not be blatantly obvious to some. I don’t even want to mention the sheer amount of times I have seen Zealots that try to cut their way to me instead of just tossing a single Stun on me and then running over to get me up.