While I do have some time for Bateman, I think his lack of size/physicality would be a major issue at test level. While he is usually pretty secure in defense he can at times struggle to bring down larger players quickly - I think he would really struggle to contain the likes of Roberts/Tuilagi (or any number of other giant international midfield backs). While Crotty may not be the biggest midfield back in the country he would have 5-10 kgs on Bateman, and is a stronger defender in my opinion. Like you I really like Bateman's skillset - he would be they best passing 12 in the country by a mile for me, has an intelligent kicking game, and seems to read the game well. Unfortunately for Bateman these days at international level these skills aren't nearly as useful for a midfield back as they have been in the past. I'm not convinced that Crotty necessarily has the ability to step-up to test level either, but I think he would do a solid fill-in job, and is less likely to be exploited than the likes of Bateman and Fruean.
While I could see the logic behind including Fruean (as he has by far the most natural ability of any of the main options) I think he has actually gone backwards this season.
Personally I wouldn't have Hoeata anywhere near the AB's side. To me he is an OK player at Super Rugby level - nothing more - indeed Bekhuis and Crosswell were my preferred locking combination at the Highlanders last season. He is good at the lineout (especially if he is used as loosie), and hits a few rucks, but is completely ineffective with ball in hand, is a bit hit and miss on defense, and still has serious discipline issues as you mention. I see he got sent off in the last Maori match, though I have no idea what it was for so it may not be relevant. While I agree that the AB's lack an enforcer I don't think Hoeata is the right man to fulfill that role. To me he spends the the game trying to act like he is the toughest player on the park when he would be far better off actually playing some rugby. This video really sums up Hoeata to me:
He gets smashed by Levi then spends the rest of the game looking for a fight - you only see a couple of occasions on the video, but there were 4-5 other times he tried to pick a fight after a breakdown during that match that I recall. In the end he is very lucky not to be sent off for a couple of swinging arms to Levi's head.....
In terms of AB's options, I do agree that George Whitelock isn't the solution either. It has been good this season to see his running game a lot more for the Crusaders / Canterbury, as previously he was completely ineffective in this area. He may not be a Kaino, Vito, or Messam in this regard, but he showed this season that he is capable of breaking the odd tackle and creating some good go-forward ball. My biggest issue with Whitelock is that he concedes far too many penalties at the breakdown - an average of about 2 per game. This would be fine if he was actually slowing down/stealing the opposition ball at the breakdown, but most of the time it is for silly offenses he should know better than to commit.