Yeah but according to you it doesn't even need a proper batting all-rounder to perform that function. Even a Tendulkar/Root level bowler can bowl a few loosening overs. You haven't explained how a batting all-rounder like Kallis as fifth bowler adds more then.
Whereas we all know that having the stronger tail and lower order depth does matter and a bowling all-rounder an averaging 28 with the bat gives you a definite edge.
A Kallis would have an even greater impact, don't understand the question. And again, you guys are the one with the all rounder label, I want versatility an extra option. Again, Hammond, Simpson, Chappell, Worrell wouldn't be deemed all rounders, but good enough for what's required.
And again, show me where, show me where one of those players lead to great teams or victories. A generous average of 15 to 20 extra runs an innings doesn't make up for having a better bowler who may present extra opportunities and bowl out the opposition for way less than that. Again, it's a negative / defensive decision.
I love American Football, one of my 4 favorite sports. The five most important positions are QB, DE, LT, WR, CB. It wasn't arbitrarily decided that those are the most important, they look at the teams that have won and what were the common factors for those squads. Yes running backs have more apparently stats, and yes a Barry Sanders or Derrick Henry would have improved any of those teams, but they still won, because even though the position is flashy and more causally evident, it lacks impact.
Similarly while it's easier to point to tangible numbers, he averages 30 with the bat instead of 18, show me where that's lead to tangible wins and impact.
I can say I've seen Gilly's innings win games, series, the aggression put the teams on the back foot.
Yes, the extra numbers look nice, but show me empirically where it's made that tangible difference. Great teams win when the batsmen takes care of business and the bowlers take wickets. In cricket the template has proven to be a good set of aggressive openers to set the tone, an ATG middle order bat leading a strong to great middle order and at least one ATG pacer and one really good second guy supported by a great cordon. That's how you win not only at home but on the road and have sustained excellence. It's aggression, it's winning.
And before the argument is restarted on if Imran / Hadlee would have made the teams better, of course, no one doubts that, anyone is taking them over Gillespie or Holding in a heart beat. But the Chiefs / Buccs would have also taken Christian McCaffrey, but managed to be dominant without.
So while the 28 looks good on paper over 17 or 18, the difference is minimal and potentially detrimental if you're going to sacrifice the superior bowler to get it.
We're looking at tangible numbers, not results and precedent. And that's because it's easier, we're stat based and easier to quantify, but I'll always maintain, that in a strong team it's so much more important to have a strong cordon that a deep tail. But no one looks at that because there are no stats and it's harder to research, harder to say but look at the average and potential. But watch Marshall, McGrath, Steyn, Ambrose, Lillee even Hadlee (in a weaker team, that's all) so much success was because they had secure hands behind the batsmen.
You have said a bowling all rounder averaging 28 gives you an edge, imagine being in a tight matchup and dropping the opposing teams best batsman, and we don't have to because I've seen it before, we all have. Who didn't experience it nearly as often are those great teams that took those opportunities and also the half ones.
So finally, yes all 3 have their place and value. But the bowling all rounder falls last, even if you're a team that consistently relies on those few extra runs to avoid defeat, then honestly you have bigger problems and not that close to being competitive. Marshall and Warne also showed they could show up when required and tough it out.
The value of a cordon is that when the bowlers do their job, that they aren't let down, and even on rough decks that odd half chance can swing a game.
The value of the 5th bowler or bowling all rounder, if we assign the tag, is at its absolute lowest, to give the main guys a rest in tough conditions and allow them not to be worn out. At it's peak, taking the odd wicket and in the case of a Sobers or Kallis the odd 5 wicket haul and match winning performance. Even at it's absolute lowest it's an undeniable asset.
In a hypothetical (and not saying it has to be)choice between top end bowling all rounder or a top end batting all rounder, most will go with the batting because you're at best the 5th option and you're not going to weaken the batting facilitating that.