You can use the network hashrate in place of diff. It's simpler.
Network hashrate is determined from the diff. So there needs to be a "simpler equation" ^^"
Actually, I've seen it many times that even the API of a coin itself has net hashrate wrong (*cough* bitquark).
https://github.com/KBomba/cuda-profit-calc/blob/master/ProfitCalc/Coin.cs#L284If you use target=24 for bitquark in that formula, you'll get the right coins/per day, they use target=32 (like scrypt and x11) in their diff=>hashrate calc.
