Mordekaiser's Q ability ---- Spellvamp issues?

As of Mordekaiser's rework, i have been having a problem understanding why his Q procs, while they trigger gunblade's spellvamp-ish effect, they do so like they are an AoE, ability giving 33% effectiveness. Why is that so? Is it because you have 3 damage instances and even if it is that, they all are single target damage instances. For example , Ekko can proc his passive on 5 targets one after another (given all of them have 2 marks etc etc) and still get the full effect applied. Why is that so different from hitting 3 targets with Morde's Q and getting less heal from each of them :/ .

Thanks in advance :)