Yes. And that's part of why he's an idiot.
You know what's easier than a dumb convoluted plan (to convince Cersei Lannister of all people to fight alongside you, as if that's going to happen), show Dany all your stab wounds and tell her about your resurrection.
At least he's pretty.
It's not about convincing Cersei to fight along side him necessarily. It's about convincing Danerys to halt her invasion and deal with the White Walkers and the only way she'll agree to do that is by establishing an armistice.