But since I don’t have enough skill to draw his famous battle frenzy, he is still presented in a quiet state, keeping Ulster borders.
By "famous battle frenzy", do you mean that part where he gets so worked up his feet turn backwards, his skin turns inside out and gets hot enough to vapourize water, his mouth opens from ear to ear, he grows a total of fourteen fingers and fourteen toes, one eye pops out, and a second tiny sun emerges from the back of his head?
Now that you mention it, haven't tried my hand on the subject for fifteen years, but attempted it in my youth and felt it came out lacking as well.
If it helps, the route I found showed the most promise was to incorporate the description of Cuchullain as "a sad, lonely little man" - somebody who is a superhuman hero compared to everybody else, but from his own point of view ignorant, afraid of himself and with nobody to turn to. That when he gives in to the warp spasm he isn't only furious, but scared out of his mind at what he becomes.
Had forgotten about it for years, but the way you depict him brought it back to mind. It is lonely at the top. Ferdiad is gone, Scathach is gone, and as always who knows what Lugh is up to? He's only got himself.