Taking the medium armor feat is not a bad idead for Wyll. I have done it, raised his DEX to 14, equipped him with the +1 medium armor available at the sylvanus grove, added a shield to his equipment and he ends up with an AC of 18 or 19.
While eldritch Blast is a reliable source of damage, warlocks are just one trick ponies with just two spell slots. I find Gale much more versatile and he can't cast spells forever as there are so many scrolls to find and buy in this game.
On top of that Gale (or any Wizard) could take the Adept Warlock feat at level four and thus include Hex in his armament of spells. Ray of Frost (cantrip) with Hex deals 1D12 + 1D6 damage and you still have the flexilibility of a wizard.
