It wasn't removed because of assassin players crying, it was removed because most of toplane's roster at the time was using it to counter Fiora and Trundle's ultimates (who were both obnoxious at the time, and the item removed their respective ultimate debuffs).
In the assessment of what to do at the time, they decided to make it CC-exclusive rather than nerfing the other aspects of the item, like the cost or cooldown. It makes sense, since it was, outside of toplane, bought primarily for CC cleanse anyway. None of the champions that had debuff ultimates got a major performance increase anyway, so in the long run, it was probably the best end choice regardless.
(Also Ignite doesn't count toward Zed ult damage because it's true damage. If all he's doing is ulting, autoing, and igniting, he won't one shot you without counterplay; he would have had to land his Q and E as well, which QSS wouldn't have helped against given its only actual stat is magic resist)