Reduce weekly requirements, to 10 QP matches (and other weeklies proportionally). Gives people with a job, kids etc a chance to actually complete it within a week.
Let the chests drop items for the current hero first, and only for random heroes if the current one has everything from the DLC.
Please, Fatshark, think about it. I understand your intention for people to not get everything immediately, which is reasonable, but even with that compromise, it takes months to get the items for just one hero, and doing all of the one-time challenges merely gives you a headstart of decking out one hero, roughly, which is a fair reward for all the challenges.