I don't really agree with VampireNaomi's criticism but I do agree that "Chikemuri"
follows a very similar canvas to "Bohyou": a character fails to protect someone from the
"villain du jour" and suffers a first defeat at his own game (gunslinging for Jigen, sword fight for
Goemon) and Lupin serves as a cathalist. The two movies even have a scene where the villain
eats bit chunks of food !
But structural similarities don't bother me when it's not completely the same.
Of course Goemon can appear stilted and distant. At this point in his relationship with the gang, he isn't their
regular partner. He does say to Hawk that when it comes to killing Lupin, he can do it himself. But the viewer can't
deny that Goemon is the one who evolves the most in the movie (which is why he is the protagonist). He starts off as being
pretty confident, to the point of underestimating his adversary and being defeated, something this version of Goemon doesn't seem used to.
And that is why he is exposing himself to this harsh training, to try to regain what he lost while getting rid of his over-confidence, of his fears (the reason
why he finally gets the upper hand over Hawk is that Hawk started to act on emotions while Goemon found inner peace).
And how can we say that Goemon is still stoic and distant when you really watched the ending ? He smiles at Lupin's remark, he protects him and Goemon
from Zenigata, returning the favour. Goemon has grown to appreciate Lupin's respect of the ancient rules while helping him as well. That's a big step !
And on the topic of Lupin and Jigen's presence in the second half, it is linked to what I said before, the respect of one's path and journey. It provides also a point of view for the audiance. You can ask me "why didn't they use Goemon's point of view ?" well for starters they did for many scenes and second, during the training part, we need an outside spectator to feel the puzzling and disturbing nature of Goemon's failures. Plus, Lupin and Jigen are clearely intrigued by Goemon's skills and personality and Lupin sees the potential in him.
To me, really, this movie is showing something more than the Jigen one while telling more or less the same things, but that's not a problem. Originality is not a quality in itself.
As for the wounds, yeah they are pretty severe and Goemon could still have scars, but cartoon characters do recover better than us. XD