It's not simple maths at all. To properly calculate it, you need to weigh up the amount of times that you kill with headshot + hit versus the amount you kill with bodyshots, then you need to calculate how much the time you save by doing hs + hit on A4 even matters because most of the time it just doesn't matter. The only time it matters if when the terrorist kills you before the A1-s would shoot its second shot, that time window is so small that it would barely ever make a difference.
Then you need to factor in the increased accuracy that A1 has, the easier spray, the smoke tracers and sound difference the silencer makes(can get you an extra kill in chaotic situations with messy comms), and the fact that Ai-s costs 200 bucks less.
It's not at all as black and white as you are making it out to be, in fact I would argue that the A1-s vastly outperforms the A4 if you weight them up against each others.