If he can learn the playbook, then this is clearly an upgrade. I liked Davis well enough, and I would have liked to see him become a good option for us, but this team is ready to contend this year. We need to fill our roster with guys that can contribute now. Davis had his chance to learn a playbook all last season and over this entire offseason (what else did he need to be doing, really). He blew it. He didn't know his protection calls, he didn't seem to know where his teammates were on the field, he struggled to get the plays called, and he made too many boneheaded moves. He could have immersed himself in the playbook like is expected of any other NFL QB, but he chose not to, and this is the harvest he will reap from that decision.
Troy Smith is more ready to go into a game and call the right protections, hand the ball to Frank and check down a few passes.