hello! morello isn't necessarily a first item, but just a situational. Actually a few games I've been building Blackfire Torch first item as it deals bonus damage for 3 secounds and also burn. Last season I usually built malignance and I constantly felt like I was useless in laning and felt like I wasn't doing anything even with poke with this item and since I switched, I felt more impactful. Morello would be more of a 2nd or 3rd item pick^^ also great for anti heal (oblivion orb).

I hope this helps solve your question

Hey! I feel that dark harvest would only be good if you're being agressive in lane and poking a lot (early game in that sense to get the stacks). I guess it would also work well depending on your ADC beacuse if you're losing lane you're never gonna get stacks D:

Arcane comet works well for me for early and late game. But it also depends on the player of course, you have your own opinion too :)

It just makes sense to have a full sorcery tree on someone like Lux, that extra AP.

thankyou!