I suppose we are all unique.
I'll answer your question with a strawman (lol) and say how many cricketers in test history have the opportunity to command a place in a good test XI on either batting or bowling? Chris Cairns, Jacques Kallis, Andrew Flintoff, Shakib Al Hasan, Daniel Vettori, Kapil Dev, Imran Khan, Garry Sobers, Tony Greig, Brian McMillan and Vinoo Mankad are 11 cricketers who could demand a spot as either bowler or batsman at various times in their careers.
I rate Miller highly, he is clearly one of the best out of the names I've just mentioned, but I think you overrate his batting a little, 7 tons in close to 90 bats doesn't command a spot in a top 6 at ATG level. I rate his bowling highly though, sometimes I think he is underrated with his bowling.
Yeh, I get your point. I'm not a blind advocate for Miller, but I think he was pretty special in terms of being a cricketer. And in my opinion, he is the complete all-rounder.
Had he not been a bowler, he would've been selected as a top 6 batsman. And I can only speculate on this, but I think his test average as a batsman unburdened by bowling would've been a lot closer to 50 than it was. He was a proper top 6 batsman, unlike some others mentioned.
Also, he was without doubt second choice bowler for Australia in his era, and some would argue he was a better pace bowler than Lindwall.
Regarding his wickets per match ratio, he was actually very cleverly captained by Bradman and Hassett. Used as an opening strike bowler for fewer overs than he might've bowled, with Bill Johnston and Lindwall doing the heavy work. Admittedly he had back problems which probably stopped him bowling more than he did as well.
Many of the players listed (Dev, Vettori, Cairns, Khan) were not really top 6 batsmen, and spent a lot of their careers at 7 or 8 in the batting order. Similarly, it's debatable whether Greig or Sobers or some others would be selected as bowlers without their batting. Possibly, but maybe not.
As an overall package Miller was undeniably good though. Top 6 bat, genuine opening bowler. True all rounder. Giving a team the ability to play two spinners and three quicks.
Sounds easy to rate players highly when you decide they were better than how they actually played.
Why not pick players who delivered on their intangible "ability"?
I don't think i'm really saying Miller was better than he was. I'm mostly saying that as a cricketer he adds a ridiculous amount of versatility to a team.