I use Starter/Grower or All Flock for my entire flock. I have roosters, chicks of varying ages, and layers. So it makes no sense for me to buy one feed for this one, one for that one, and another for the rest. They won't stay out of each others' feeders anyway. I supply oyster shells in a separate container for the layers. I've had no issues the years I've been doing this, and the chicks grow well, the layers lay well and the roosters.....well, the roosters roost well.
I want the higher protein for all of my chickens.....they molt faster, feathers are stronger, and they can withstand our harsh winters better. And feather eating, where they seem to eat every feather they find and then peck the feathers off flock-mates, is usually corrected with additional protein so why not try to prevent the problem in the first place?
If you are concerned about the weight in your chicks, a few things come to mind. First of all, this is kinda the age when their growth is unbelievably fast, so it may well be nothing at all to worry about. They tend to look "rounder" at this stage. You could also rethink how much they eat. Lots of people fill the feeders in the morning and then adjust the amount they feed by checking if the feeders are close to empty at the end of the day. You could try "fermented feeds" too....lots of threads on here about that so just do a search in the search bar. And last, you don't say how many treats they get or if they free range at all (at 5 weeks old most folks don't do that yet, although mine are out at just a couple of weeks old) and base on their food intake accordingly. Treats are treats....they don't need them nor should they have them constantly.
Good luck! And WELCOME TO BYC!
Edited to add: @keesmom , we posted at the exact same moment! Haven't crossed paths with in in forever! Good to see you!