The Silent Legion
When you defeat Warmaster Seerus he drops a mask fragment, with that fragment you can craft a mask for you to use at an anvil at the lobby of the mission.

The same should apply for The Silent Legion. After you defeat Arkus he should drop a fragment of either his armour, mask or sword (just one) so you can craft it later. Since this is just a rank mission and not an expansion one like Operation Crimson Hammer, the reward should be just that material and the chance to craft the item, no weapon rewards for just doing the mission.

Jelly Green Giant
Also i think there should be a mission where you have to fight the jelly green giand. And maybe the same as i explained above for this mission, you get a unique material and you can craft something like jelly green giant shield or something like that.