To make it obvious that he looses all hope.
Maybe the broken chains does not mean that Guts is overtaken but that he is not influenced anymore by it.
Also when Guts lays down like an infant it may had been used to symbolize that he is in a state to be born again.
I think you are right about Od...
I think that this episode was too important to get in the "Tao" and "Ki" thing that Miura said at an interview to Yuji Kaku in 2019.
Google translate this :
https://sp.shonenjump.com/p/sp/1903/jigokuraku_interview/
it is in page 2.
What I am afraid of is that Miura probably planned to do something unpredictable and if this continuation does not appeal to the hard core fanbase, his final vision may never be accepted and treated as fan fiction.
As for me I feel delighted that I am going to get close (by reading what is to...