6 AWG wire melt down

It could be that some strands inside the group broke when the extreme bend was made. When needing to shape heavy cable in tight spaces or areas where space is a problem, it is best to leave the cable long and then shape the bend before cutting and fitting a terminal. After bending a turn, it's interesting to see how different the lengths of strands are at the bitter end.
There's a lot of science on current conducting capability of stranded wire. A great deal of the current is passed from strand to strand laid alongside. Think in terms of the conducting taking place from the terminal to the outer strands.
Welding cable is famous for it's supple nature compared to battery cable, but that is because the strands are not continuous. Just a lot of shorter lengths laid alongside like bricks, only longer and bundled by insulation. Yes, the rubber is also more supple than Vinyl covering, before anyone protests.

I keep learning something new on US electrical components.
Here you could only find that connected to a terminal strip (hence my suggestion of heat dissipation on that side), 'cause breakers are designed to take the bare wire directly.

Stepped in What??

Feast your eyes on this specs sheet, inclusive of a technical drawing on page 3.
https://www.gewiss.com/content/dam/gwdam/FILE/ZIT/ct_serie 90 mcb_rev2.1_en.pdf
That's just one among many producers, but the connections arrangement is pretty much the same, also because they are designed to be attached to a standardized rail.

Many years ago I found a few of these mounted on a Din Rail.
One went to the ships A/C pump.
It was a nice installation and I thought it was a cheap fix added after factory.

It was Hidden behind a beautiful and proper breaker panel in a Viking Sport Yacht (Princess).

Now you show me the same, reflecting a tude that this is a normal marine breaker?

Oh gad I need to retire from this madness,,,,
Oh wait,, I did!!

Well, I've seen boats built with breakers like these 30+ years ago and still working with all the original ones as I'm writing.
I'm not reflecting anything, though. You asked, I replied.

Besides, you recently posted in another thread an impressive list of breakers faults that you are used to live with, which I never heard of before - and some of them would trigger penal responsibilities for the component producer on this side of the pond, BTW.
So... Your point is, exactly?

Interesting.
Obviously neither Lazzara nor the builder of my own tub asked CR approval...