Re: solids substitute or sumplement breastfeeding?
That's my understanding as well. My ped also told me that BM should be her main source of nutrition until at least 1 and before that solids were really more for experimenting, getting used to new tastes/textures, etc. I was also told to offer BM before solids so baby didn't get full before nursing, though this never seemed to be a problem for us.
One reason I can think of that it might be more of an issue for breastfed babies rather than formula fed (this is just my guess) is to prevent a decrease in your milk supply.
Having said all that, I know that when my dd was away from me she would eat more solids at day care. She more than made up for milk intake when she was with me, though. She nursed A LOT in the evenings, nights, mornings, and weekends.
“We are not put on earth for ourselves, but are placed here for each other. If you are there always for others, then in time of need, someone will be there for you.”