You are dissatisfied by this, so am I, but I understand SE logic here. The desire is have people play as many roulettes/dungeons/trials/raids/etc... as possible. Thus, if you received both the Tomb and Levelling rewards, you need to run X less runs to get your stuff done for the week.
They have done a very decent job in maintaining relevancy for old content with the roulettes, quests turnin, Relic, etc.... The reward separation, just continues along those lines.