Grubblies pellets looks like a mixed type feed- it has pellets then loose grains correct?
Try soaking it or fermenting it. He may be picking out the grains and not eating the pellets. Looks like it's 16% protein.
What is the "highly recommended layer mix" - a photo of the bag/tag analysis would be good.
His feathers are rough looking because the hens are plucking at him, they are nipping the tips off his feathers. Probably eating them - could just be a bad habit, could be nutritional deficiency.
I'd consider feeding an all flock feed that is 18-20% protein, severely limit scratch - yep, I know the kids want to scatter something for the chicken, give just a little bit every few days - they forage and free range and get veggies too, so cut down on that stuff and focus on them eating the normal feed and see if he starts acting better.
There's nothing you can do about those feathers = he will have to go through a molt.
And check his crop - make sure it's emptying overnight.