I sorta like how you switched around Arthur and Lancelot as Arthur being the "quest guy" makes more sense to me. Lancelot's new ability seems very appropriate to him as he is sorta like the perfect knight in the legends, but also kinda independent. So I like the idea of him being this constant six that you don't even roll.
But yeah, if you like my idea for Leo then please try it. I think it'd be cool as there is currently no "building guy".
I wonder if Percival could use a buff or not. I was thinking he would always kill one army monster per turn, regardless of if you did one of those missions. He'd be sort of like the balista, but free. I dunno who he would target though (randomly, strongest, your choice, etc).
Maybe instead every turn, he would remove one of the dice required to complete a fighting mission of your choice?