The issue is Wyll was rewritten too close to release. It's pretty much the same with Halsin, who was only included last minute and as a result is very bare bones in dialogue and quests. A lot of care and effort went to the female characters, with multiple Acts spanning their story arc. The only male character who got similarish treatment was Gale. Wyll and Astarion got very slim pickings, though Astarion at least gets some interaction with Raphael in Act 2. But Lazael and Shadowheart just eclipse the other companions by a mile, and Karlach has enough of a loud following that she's getting fixes just like Minthara and probably Astarion will.
Honestly, Lazael should have gotten her time with Act 1 at the Creche, Shadowheart her Act 2, and the other companions should have gotten more emphasis in Act 3 to compensate. But the story just stayed mostly Lazael and Shadowheart focused with Karlach in third place.
