If you refer to the article below, Imran's performance in the 1982 series against England is considered the best ever in terms of all-round output, followed by Sober's in the 1966 series against England.
https://www.espncricinfo.com/story/_/id/22034780/top-allrounders
I think posters are seriously underestimating how difficult it was to average 35 plus in the 1980s.
The only thing that article showed is that Gilchrist is quite possibly the 2nd greatest all rounder ever, and that in terms of performing with both bat and ball over a career, Imran is closer to Kallis than he is to Miller far less Sobers.
Note the article that you introduced.
Imran Khan to me is the best bowling all rounder of all time, but his batting is a tad over rated here.
He played a little over 20 years of cricket but yet scored only 3807 runs (less than 200 runs per year). Something to do with his batting not good enough for a decade or so and blossoming late, but still a striking stat for me.
He played 5 series of 5 tests or more (one of them was a 6 match series) and yet only scored 300+ runs in a series once in his career. Miller and Botham did it 4 times, Kapil did it twice.
Yeah, Imran's batting isn't only overstated, but overrated. It's a problem that Kallis's bowling production went down as his career progressed into its later years, but not that inversely, Imran's batting improved in his later years as his bowling also wasn't quite the same. His latter career numbers, not outs and down hill skiing boosts his numbers to where they are and even his rpi of 30 is boosted by the former and the latter.
Minnows are brought up for Kallis, but not that all but one of Imran's hundreds came in draws, and even the match they won wasn't nearly a match winning effort. Yes a couple were clutch match saving efforts, but when your knock is the 4th century in an innings, there might be some slight stat padding at work.
And as for the argument that he was a top 6 specialists batsman, that's a little rich as during his bowling peak, he hardly batted at 6, and even over the course of his career the significant majority of his batting was done at no. 7, and he batted at no. 8 more than he batted at no. 6.
Conversely Kallis was first change more often than he was 3rd. Like Imran the vast majority of his career he spent as the 4th bowler (equivalent to the no. 7 bat), but played more as the 3rd option than he did as the 5th. The inverse of Imran.
Similarly though, in a normal cricket team the ideal spot for Imran would be an at or just below test standard no. 7 (let's say just below Knott level), and Kallis a similarly rated 4th bowler. Push both down a slot and they're above replacement level.
In an ATG scenario Imran is a useful no. 8 and Kallis a useful 5th bowler. Kallis though also being able to add to his value by being an AT Great at the critical 2nd slip spot where there would be no depreciation of skill or output.
But for Imran's batting and Kallis's batting, they're basically the same.