What to feed very pre-term babies is not clear, and yes, fruitful, there has been a recent overview (in the BMJ, I think) which called for more research. Pre-terms need to grow and to grow rather faster than they would do in utero - the growth factors in donated human milk are not sufficient (because the milk is produced for healthy, term, older babies). However, there are anti-infective properties in donated breastmilk which are not present in pre-term formula and these may well boost the immunity of pre-terms to a potentially fatal disease called necrotising enterocolitis (NEC).
This over view pointed out that the research showing donated milk lessened the risk of NEC was done not on very pre-terms.
So....it may be that the best nutrition for very pre-terms is donated breastmilk plus a fortifier (special cows-milk-based booster). Or it could be that initially at least, pre-term formula is better, with donated human milk (or of course, and better, the mother's own) being introduced later when the very pre-term is a little older.
I don't think it is clear cut, and the research should be on going. I don't think our support for bf should blind us to the fact that some babies are not 'designed' to be outside the uterus and that when they are, they may need artificial feeding (at least at first) in the same way as they may need artificial respiration and so on.