I've seen everything you list there for Cumberbatch. I've seen about everything the guy has done since 2005. He's stiff. I agree with you that he would make a good Master, but he is a limited actor.
I haven't seen the two films you mention for Caine. I'll check them out.
Your inability to think outside the box when it comes to an actor's suitability to a role isn't my problem, so why do I need to "support" my "thesis"? We're going to disagree on this all day, so there's no point.
I have an inability to think outside the box because I can't see an actor who has only ever played brainless tough guy roles play a brainy mastermind? I love Dwayne Johnson, but I wouldn't cast him as Lex Luthor.
Is it failing to think outside the box to know that Vin Diesel would make a lousy JFK? Or that Jason Statham wouldn't be the right guy to play Sherlock Holmes? Or that Arnold Schwarzenegger wouldn't be a good Captain Von Trapp? These are actors who are known for playing a certain type of role, and don't really venture outside that territory.
We only know actors by what they've done. Sometimes that's powerful enough to show us they can do more. Matt Smith's small role as Jim in The Ruby in the Smoke
was nothing like the Doctor, but I could see the potential there.
But what Craig has done, the body of his career, has shown me he can play one type of role. I've never seen him try to do anything else. Let me see Craig play something off type and do it well, and I'd give him a shot. When has he? If Craig has ever wanted to play something different, I'm sure he's had the chance. Name one performance that has shown us something more than "tough guy." Please. I'd like to see it.
You think Cumberbatch is limited, fine. Maybe I'm seeing degrees of subtlety and nuance in his performances that you aren't, or maybe I'm just reading into things. But in any case, limited or not, he's shown that he can play the same type of role as the Master. It's in his wheelhouse. But on the other hand, I wouldn't cast him as Jim Kirk or Wally West. That's not failing to think outside the box, that's recognizing what an actor's strengths are.