Being raw isn't necessarily what the defining factor is. Aaron Rodgers, Donavan McNabb, Steve McNair, Troy Aikman, and several others were all unpolished quarterbacks when they were drafted.
David Carr, Sam Bradford, Carson Palmer, and Peyton Manning were about as polished as it gets coming out of college. Only Peyton won a playoff game and it took him 6 years to do that.
Locker was more raw with his footwork, but had a special set of football intangibles and knack for making the players around him better. He was a clutch player who was comfortable with taking the game on his shoulders when he had to. He elevated a team that was 0-12 without him to a 6-6 record. Locker wasn't even supposed to be playing after the Oregon St. game towards the end of the season after he suffered broken ribs, but kept playing because he wanted his TEAM and his SENIORS to finally feel what it's like to be bowl eligible. He led those outmatched scrubs to a bowl victory over a supremely talented Nebraska team.
Tannehill is only more polished in terms of tying his footwork into his throws, but his arm isn't as quite as strong as Locker's, release isn't as fast, and doesn't elevate his teammates the way Locker did. He didn't have any mechanical flaws in his throwing motion, only lack of polish in his progressions and footwork, which is why he was a top 10 pick. During his limited playing time as a rookie, he led all rookie quarterbacks in QB rating.
Like I've said from the beginning, if a team is comfortable taking Tannehill in the top 10 with the understanding that they're passing up elite players in order to do it... go for it. As a football team, you're the one that has to look yourself in the mirror afterwards.