I take it (after a few glances) that your green/red expectations are purely on whether the values rise in the cycle of Copper, Bronze, Iron, Steel, Adamantine? (And you haven't placed Silver, yet.)
I think (based on those same glances) you'd have fewer reds if you started with Cu, Fe, CuSn, Fe++. Mere iron is second in line of that subset more than it's third, and that gives an element, element[1], alloy (of first element) and alloy[1] (of second element). Which doesn't 'explain' anything, but is more logical.
Spoilermetal does indeed spoil the pattern (because it's mystical, probably, and inclines to physical rules with far less of a nodding acknowledgement of our reality than the others). Set that aside for the moment.
And Silver's odd, too, as it looks like you discovered, not botheting to fit it in. I haven't done a full tot-up of its optimal ranking (for least overall hiccoughs in the series) but individual qualities ask it to appear anywhere from before Copper to even after Steel. Likely it sits most comfortably/least uncomfortably immediately before or after iron in my suggested relocated position.
But that's in overview. There should be no all-rounder ranking all different physical qualities. If you pare it down to "light and deformation-resistant", for proof against certain types of weapon damage, or "blunt-forceful and not fracturable" for use in certain attacking implements, then you can perhaps come to individually different rankings for each use. As others have already done, IIRC.
Some games do treat it as a basic sequential ranking. Wood<Stone<Iron<Gold<Diamond or somesuch, ignoring that gold armour is probably stupid (or, at best, better restricted to decorative filligree to a more substantial iron-based main mass, just to show off) and I'm not sure I'd trust a diamond helm (more than most of the others) against a warhammer and wood of the right sort definitely has its uses (best stuff for a longbow, I suggest, and often not that bad at all for a pure blunt-force attack that doesn't rely upon edges or points specifically vs stiff metal protection).
But there's a rock/paper/scissors nature as well, here. Not entirely balanced/absolute, like a true RPS-derivative, yet you're not left with a totally third-rank material (especially if you include availability and production capability to your metrics) that you should just forevermore ignore once you have started to be able to use second- and/or first-rank materials, or are encountering enemies who have.
At the very least, if you're planning on deciding your own good/better/best system, first split it into separate weaponry and armour categories, before then considering sub-dividing further, and calculating what values are better-high vs better-low for each subset you'rev considering. Or just straight crib from the work I'm surs is already posted in the Wiki.
[1] Ok, not exactly, with how iron and steel are, IRL, but it suffices for this case when we don't fully know if its wrought or cast iron, and there's steel and then there's steel, and apart from the slagging off of impurities we don't know (nor do the dorfs, I imagine) if we're talking about chrome/moly, austenitic stainless, etc...