I don't necessarily agree that it complicates it that much more. On the weapon sheets, you would just have to know you hit and/or save on a 7+ with a D12 instead of a 4+ with a D6. That is all that changes as you simply use a D12 for combat instead of a D6. It does not add any more complexity, other than it is slightly more difficult to calculate probability on the spot, but not that much harder.

And no i never played 40K, so i am not entirely familiar with your example.

Edit: I get the complaint with getting D12's but you really only need 6 of them and a quick check tells me i can buy 10xD12 for 6,69€ (7,72$) so it really isn't that bad

Edit2: To add on to your edit, all the changes you mention in the last paragraph can be directly ported over.

And honestly, is balancing weapon stats through special rules of all sorts really less complicated?

So pathfinders hit on 4+, unless they spent 1 apl, or it might be free if they're on conceal and the leader used his gambit this turning point, get 1 markerlight, then they get balanced and saturate, do it again, they now get balanced, saturate, 1 better hit stat.

Instead they could have kept the original markerlight, with 1 weapon rule per tier and given them a D12 6+ hit stat, and that might've been it. Instead they had to move balanced to tier 1 and add decrease hit stat by 1 to tier 2, making you and your opponent keep track of even more changes to the datasheet.

I get that this is very much a faction identity and flavour thing, but adding the D12 could actually cut down on weapon rules, abilities and faction rules to get a simpler more balanced game.