I’d rather see the kill contracts split into:
Kill Scabs
Kill Dregs
Kill enemies with melee
Kill enemies with ranged
I support the tiered contract system, and would like to have the weekly bonus be tiered too, but with a point system.
So completing Tier 1 on one contract gives 1 point, T2 gives 2p, etc. and have the bonus require 6 points for T1 reward, 18p for T2, 36p for T3 and 48p for T4. That way you can get some of the bonus even if you hyperfocus on a few contracts, get the corresponding tier bonus for completing all contracts at a lower tier, and getting all the bonus if you finish T4 of 3 contracts and T3 of the remaining 3.