Why warlock/wizard?
Would sorcerer be better since both are charisma based?
It´s to use a mechanic trick. Abjurer wizards have a protective shield that is recharged using abjuration spells, so the build picks one level of warlock to be able to cast the warlock spell Armor of Agathys to recharge the barrier, at least I assume that is the selling point of the build if I guessed right.
I guess you pick githyanki to have access to medium armor and some martial weapons.
That also assumes that the DM lets you use spells from other classes to recharge your Arcane ward because the manual does not forbid it.
Other builds use mage armor, shield, ... or the ritual spell alarm to recharge it between fights, which is less efficient.
http://dnd5e.wikidot.com/wizard:abjuration
https://www.dnd-spells.com/spell/armor-of-agathys
For a lv 10 char I am not sure if 1 (or even 2) lv warlock is worth losing bard 10.
The bard could select 2 more spells from another class and become expert in more skills.
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With a level cap of 10 I´d go bard 10 because of the level 10 features: Bardic Inspiration (d10), Expertise & Magical Secrets. No contest.
