But in the history of cricket there have been several cases where this has been achieved.
Sure, about 30 cases of a team making 130 with 5 wickets in hand out of about 2700 odd ODIs, I'm sure there are a few more among an even greater number of List A games, but the fact is that it's not happening a lot. To say this is an important figure is to disrespect the importance of bowling in limited overs.
Like you said, in yesterday's game the all-rounders brought the score up to something respectable, but the game was lost comprehensively. When the time came for those all-rounders to bowl, they were punished with impunity. You can scarcely cram any more batsmen into that side either, they bat right down the order. However, if they want to defend 200 more often, they will need to bowl a lot better.
It highlights that a good team needs both good batting and good bowling at the same time; a player who both bats well and bowls well is not common. If your 5th best bowler has an average of around 45, you know without having to think about it that you're going in with weak bowling and that's as much a risk as any.
My original point though, was just about common sense. I wasn't saying that all-rounders and number sevens have no role in the game. I was saying simply that you can't overlook the importance of the six batsmen who have to bat before the seventh. In the event of such a batting collapse as on Monday, it is not the number seven's failure if the game is lost. He has less chance of nursing a team through a hundred runs to victory than a bowler has of taking 6 wickets. It would be very specious reasoning to say that Australia A won the second game because they had seven batsmen. It was just a good performance (I hesitate to say "all round"), the specialist bowlers bowled better, the openers fired and not even a middle order performance was required.
One game in fifty might be winnable through an enormous rear guard score and fair enough if you have a team that can pull that one out, but you can't structure your team solely around winning 1 game in 50. The conventional way to win is with those upper order batsmen making runs. 7 batsmen aren't always necessary (and importantly, ideally not necessary) to bat out 50 overs, but you do always need 5 bowlers for that.