My main problem with Wyll is, that he is very squishy. I could keep him at the sideline to cast Eldritch Blast but that does not seem quite what he is supposed to be. Maybe I just have to get used to the class more.
Warlock is a great class, he has access to some spells that trivialize some fights. You can also multiclass him with paladin or sorcerer.
I have now multiclassed him with Paladin and a dip in Sorcerer (for the flying-feature) now, put some light armour on him and that amulet with the Shield spell. Shield-Spell desquishyfies everyone. And it started getting fun.
I like my camp full, but - in case this is how it works now - I will gladly switch Halsin for Minthara after lifting the curse in Act 2.