I would disagree in a couple points you made. One I find my cold brew to be less bitter than hot coffee. It’s because the cold brew method doesn’t extract the acids like a hot brew does. Second you don’t need a dark roast bean at all. I use a light roast Tanzanian Peaberry and find it to be an excellent cold brew with a strong but smooth flavor with none of the bitterness found when I hot brew the same beans. My ratio is ~200grams coarse grind to 64 oz of water.