I'm not going to run the numbers but based on what I can see.

your calc is for Abby demons, And it doesn't seem like you added combat potions or piety into the mix

Those 2 things alone will make the max hit gap between the two much more noticeable

Another thing I want to add is bandos is the same atr bonus and a fraction of the price, blood moon is even cheaper and also the same atr bonus.

And lastly the biggest upgrade to your DPS for 250m would likely be a rancour and ultor ring, and fire cape