Right leg is a bit weak, perhaps due to injury.
Take a look at the right leg and foot again for any green bruising and at the very back of the leg along the spur to see if there's an abrasion. With dark legs it's sometimes hard to see bruising, it can be very subtle.
His spurs are fairly long, so he may have bumped that one and it's very sore. Spurs that get hit or damaged can be painful, think of stubbing your toe or bending back a fingernail very badly, how it can be sore for days.
He's a big beauty. I'd try to continue with the vitamins. Since he's so large, he could probably get 2cc rooster booster daily, since the direct oral dose is 1cc per 3lbs of weight. Do you think he's about 5-6lb or maybe a bit more?
Give him some extra protein like egg, fish or meat. The mealworms are fine, but go easy on them. I'd focus on him eating normal poultry feed for most of his diet, but the treats you are giving kale/blueberries are o.k. in small amounts.
He looks to be in pretty good shape. Do you think you could keep him or bring the others to your place? Might work out better, but it's understandable that you may not have space/housing to do that.