So,at the end of HiPoS the return of our investment would be 312$,which is above the 306$ that we initially invested.
And we would also have our 75000 coins to have them staking for 1% annually or do whatever we want with them.
The flaw in that thinking is discounting human nature. If everyone does that, they'll create too much sell pressure to regain their initial investment, therefore lowering the price of the coin.
Of course not everyone will stake and other things could occur to increase the price of the coin. But it does have a pyramid feel to it ... basically whomever sells their coins early (after HiPos) will get their initial investment back, but if everyone tries to sell, it'll be too much selling pressure and not enough volume/buy support to pay them all.
So yeah, in theory your model could work... for some.