I don't see how the loss of an identikit fried chicken shop and the addition of an independent fishmongers can be detrimental to the local shopping options, especially when there's another fried chicken place still in business a few doors down and a trip into Brixton was required to buy fish prior to the new place opening. I've only been in there once so far and the guy was very pleasant, knew what he was talking about and gave me a great cut price deal on some scallops as he'd run out of what I was originally after. So all good if you ask me.
As for the florist, I'm assuming you mean the flower shop on Dulwich Road, not the lovely lady who sells flowers out of the old barbers (used to have her stall outside the Half Moon, then the timber yard). As far as I know, the Dulwich Road shop mainly focuses on weddings and the like. So a different target market. Again, not sure what's wrong with that, they're obviously not interfering with each other.
I'm not sure another bakery was really needed, what with Blackbird and the one on Half Moon Lane but better than the chicken shop it replaced. And a bit of healthy competition for Mimosa from the new deli won't be a bad thing as it's always been a bit pricey. Moses' move from CHL has already been explained.
If the new fishmongers had replaced a perfectly good old one and just upped the prices then that would be wrong but I think Herne Hill's got a great mix of shops. Some are more upmarket than others but at least they're all independently owned and seem to care about what they're selling. Calling these places "posh" is a bit lazy. Fish, bread, cheese, flowers and fried chicken are things that everyone enjoys from time to time, having a bit of choice is no bad thing.