I don't think an obvious choice necessarily means its the wrong choice.
Jack Nicholson, Danny Devito, Patrick Stewart, and it could even be argued Christian Bale, were all the most obvious choices when they were cast .
I include Bale in there because he was a fan cast before he was got the part , and it was between Bale and Hugh Dancy.
Dancy would have seemed more of an outside the box choice as opposed to Bale if Nolan wanted to go with a less odvious choice.
At the same time, not every outside the box choice works , such as Jessie Eisenberg as Lex, Topher Grace as Eddie Brock, etc.
Sometimes the obvious choice is the best choice if the actor or actress is good.
Sometimes the outside the box choice like Ledger is the best choice.
It can go either way.
The commonality between the outside the box choices, and the obvious choices is that , alot of times, as with Nicholson and Stewart, and Ledger and Pattinson, they're good actors regardless of whether they're the obvious choice or not.
Now if we're trying to predict the type of actress Reeve may want , then perhaps, an argument could be made that he won't go for someone who would be the obvious choice.
But a good to great actor or actress being an obvious choice , to me , doesn't mean they'd be wrong for the role.
At the same time, whoever the actor is , they're going to be acting to the role as written anyway, so even our assumptions about how an actor or actress would play a role, might not resemble their actual performance.