When I'm talking about the Beast, and Guts "giving in to" or "choosing the path of" the Beast, I'm not really talking about the armor.
I figured as much, but to me that shows a confusion about what the Beast of Darkness is supposed to represent in the story. There is no "path of the beast" that is viable for Guts to follow. It is something within him that he has to fight, and presumably to eventually tame, lest he loses himself and everything he holds dear. Ever since the titular episode, it has been presented as a point of no return for him, which is why he was never going to actually "become the Beast" as you say.
As far back as its first appearance in episode 118 it has been hinted that Guts' life of revenge has sown the seed of a growing monster within him that parallels the monsterous or bloodthirst aspects of people who become Apostles
I don't think you can say that it parallels people who become apostles, no. That's a simplistic notion that doesn't fit the facts of the story, where not a single apostle whose backstory we see is shown sacrificing merely because they're bloodthirsty. What the Beast of Darkness is associated with is the persona of the Black Swordsman, a man deeply traumatized by the Eclipse and who will do anything for revenge.
Puck veered him away from that path enough that he could heed the call to go save Casca when it came. Since then he's moved farther and farther away from it, but the trauma and associated madness are still there under the surface. Not much of a problem in normal circumstances, but dangerous when wearing the berserk's armor.
Because Guts himself has the Beast within himself regardless of the armor, and given the foreshadowing, I don't see a different approach to his use of the armor really solving the fundamental issue. And as long as the focus is on the armor and not Guts' psyche, the status quo is not going to change.
Well that's obvious. I've talked about this many times over the years. His trauma needs to be healed (much like Casca's), which will go a long way in helping him use the armor more intelligently. The two go hand in hand. The armor will never be safe to use because of its nature, but taming the Beast of Darkness would have become necessary for him to keep using it at all.
if he resolves the Beast issue through some deep soul-searching without ever mentally becoming like the beast (independent of the armor) then the temptation will amount to nothing except the armor was the danger.
I don't think it's true at all to say Guts absolutely
has to "become like the Beast" without using the armor or the danger it represents would amount to nothing. It's like saying because Guts never died in the story, he was never in danger of dying. Like I told you above, the Beast of Darkness represents a threat from within, it's not meant to be a valid option he could pursue. And we've seen him give in before, when he bites Casca's breast in volume 23.
If there was no chance of Guts mentally turning into the Beast of Darkness under any circumstance without the armor then that would make the Beast a non-issue if not for the armor.
Without the armor, the Beast of Darkness would be a minor issue after he accepts new companions, yes. It would amount to Guts sometimes having unhealthy thoughts and impulses, maybe behaving rashly or unreasonably, but not in him killing his friends. That's why the introduction of the armor to the story at the time Miura did it was so clever. It rekindled and turbocharged the danger the Beast represents.
If you want to see Guts at risk of crossing a line he couldn't come back from without the armor, it's already been done in the Black Swordsman arc and Lost Children chapter. It's not a coincidence the Beast of Darkness is introduced right after that: it's to show that this side of him remains there, even though he's mellowed. That it can and will resurface, because he can't get over the Eclipse.
The impression I get from the imagery with the chains and foreshadowing is that the Beast is a bigger issue than just fuel for the armor.
What the chains represent in episode 290 is Guts' ties to his companions. There's no mystery about it. They are used to keep the Beast of Darkness – which represents his darkest and most destructive urges – in check. And it specifically needs to be kept in check while he wears the berserk's armor. That's what it teases him about, telling him he won't be able to do it.
And guess what happens on the solitary island, when he unleashes the armor's power? The chains begin to break... But he's stopped by his son, who dispels the darkness to show him Casca's face, before anything bad can happen. Hence what I told you in the previous post.
Since Guts true potential weakness against resisting following the impulses the Beast represents (independent of the armor) is dependent on his circumstances, i.e. the extent to which he has something or nothing to lose or even believing it can be done, that's where being able to hit Griffith or not would have bearing.
The Beast of Darkness was never concerned about whether something was doable or not. The kind of urges it represents aren't about calmly assessing the feasibility of killing the God Hand. That's really besides the point.