How does that work away the SC and especially helpful pitches?
The problem with your 5th bowling option being the a bowling all rounder is that on helpful pitches it's not as required, and now you're a batsman short where said bowling all rounder is more likely to struggle in the referenced helpful conditions. In less helpful conditions, it's likely to be a draw and you're less likely to be in a position to guarantee that, with again, a batsman short.
The 5th bowler is also likely to get substantial time with the new ball, and their primary duties are most likely shower spells to rest the front line operators and bowling in the dog overs. Seems like a waste of a batting spot, for minimal returns.
But since this is such a brilliant fool proof plan I'm sure you can point out to me all the AT selections where Imran is chosen ahead of Sobers. Where you're swapping a top 5 batsman of all time for an rpi of 27. At 6, for an AT squad.
And if not Immy, who is it, Pollock, Vertori, Jadeja? The only viable option has ever been Miller and even that's questionable.
And just so that we're clear, a better bowling attack is based on quality not quantity.
A thought process obviously lost on you.