Brahmas feather in incredibly slowly. I fed 28% protein and never had a picking problem, yet had a cockerel have a completely bare back until 14-16 weeks. Most of my Brahmas have saddle feathers under their main cushion of feathers by ten weeks but you would have to know what to look for and search for them. I would expect most any other breed (minus other slow growers like Cochins or Orloffs) to have them emerging by ten weeks assuming they've been fed high enough protein for feather growth.

The 8-9 weeks estimate seems entirely plausible, especially if the Brahmas were from a hatchery line as they growth much faster than my birds did!