The advantage for Mitch is that he picked up cricket fairly late in life I believe, so you would think he has more to learn - especially about batting. At the moment he's just a former tennis player with a good eye, good technique and strength to hit long.
I can see him as a Richard Hadlee or Wasim Akram or Shaun Pollock type batsman. Hadlee started at #8, but often batted at #7, - probably a stretch, but in the 80s he had the reliable Ian Smith below him to solidify the order. Akram sometimes made it to #7, but mainly played at #8. Wasim had huge amounts of talent, but so often threw his wicket away. Pollock was like Hadlee, playing a fair bit at #7 but more often at #8 to make the SA batting lineup insanely long as Boucher sometimes played at #9.
But those 3 guys could be called comparable or even better batsmen than their keepers. Hadlee beat out Ian Smith for #7. Wasim Akram would sometimes bat ahead of Rashid Latif or Moin Khan. Pollock used to bat ahead of Boucher, but Boucher passed him later on. Mitch is never going to outbat Brad Haddin I would think. He might outbat Haddin's replacement/successor though. Depends who the Aussies go for.
But Mitch certainly deserves the #8 spot, and going on current form a Brad Haddin/Mitch Johnson team at #7 and #8 could be 2 of the best batsmen to play at those spots ever.
Overreactionary?? I don't think so. The best pure #8s of recent times are probably Ian Smith, Danny Vettori and Chaminda Vaas. Mitch has a very good record compared to those guys.
And at #7, Gilchrist is the leader in history but after that you'd have Alan Knott, Kapil Dev and...maybe Imran, Chris Cairns, Jeff Dujon. But Haddin would have to be up there with those tier of guys at present.
And yet the Aussie selectors want to lengthen the tail by putting McDonald at #8
