Breastmilk is still better than formula, even today's standards of formula. One of the very cool things about breastmilk is that it becomes more nutrient dense as the baby gets older, whereas with formula, you need to give the baby more and more of it.
Another thing about the weight, all of the expected weight charts are based on formula feeding. You need to use separate weight charts for breastmilk only weight gain. If you are breastfeeding, it's common for doctors to incorrectly suggest you supplement the breastmilk with formula because your baby is "underweight", when they actually aren't. Supplementing with complex carbs like rice cereal is also probably not very good for your baby, with no real upside.
Strategy that we are going with is no complex carbs at all, just supplementing with steamed veggies and fruits now that we're onto solids.
My baby was failing to gain weight at all (discovered with baby scale at home between appointments), and once I started pumping, realized that I wasn't producing much. With an aggressive schedule, I got to an adequate level. We supplemented with formula until I was able to cover all demand.
