To address your original question - I understand the best exercise for weight loss is actually fairly moderate, but steady exercise. Did you use heart rate zones for rowing? I'm not sure how different your cycling zones would be, but zone 2 is supposed to be good for weight loss - the thing is that at high levels of exercise you burn lots of carbs and less fats, at the slower, steady levels you burn more fats, resulting in more weight loss. The caveat - we are all very different with different metabolisms, so this is really really ballpark unless you go and have some sophisticated metabolic testing done.