Do you get to walk through any of that background of Order 1886 or is it all just a matte painting?
No, but you do in these segments. The game is obviously not nearly as large as RotTR, but there are some larger areas within in it, that do not stress the engine or lend to any frame drops. In addition to that, RotTR whilst admittedly gorgeous, definitely drops in visual fidelity most of the time a lot is on screen, notably with bigger draw distances or larger environments.
Also, I find that in RotTR, outside of cutscenes, when there's no muck on Lara's face (e.g. blood, mud etc), the character model can sometimes look quite bad in comparison.
Though in the right lighting and conditions, when you're not up too close and when her model has a bit more texture diversity going on, Lara's model can look impressive.