Hey bro, whatsup, I did not talk about me (although I look small because I'm skinny lol), only I see that many are conditioned by the structure and sideways have a good arm but when they are facing forward it seems that they have a skinny arm
My problem was never a brachialis issue as I worked out with a guy who was a world champion arm wrestler.
We got plenty of forearm and indirect bicep work.
My issue was just plain lack of thickness. Only when I started doing heavy curl work that targeted the inner biceps did my arms seem to start to develop that fullness and "meaty" look.
Biggest thing that helped me was progressive weighted chin-ups with palms facing me at a normal width. I still start biceps off with these.
Mine have greatly improved, but I've also come to the conclusion that my shoulders got the better genetics of the two muscle groups....and they always make my arms look small when viewing them from the front!
That I think is what built mine the most. Real heavy bent over rows and weighted pull ups built mine up. I never did a single hammer curl or any exercise that concentrates on the brachialis. I don't think you really have to when you train heavy like this.