Good Morning All
To start with, there is no issue with constructive feedback on asset creation, be it to a specific creator, or the community in general (as in this case). If we took the approach of not allowing constructive feedback, well, we wouldn't see any improvement.
If you aren't prepared to take the feedback on, then that is fair enough. The OP isn't forcing people to change their ways, their making a constructive comment on the textures on many available assets that are modeled well, but could do with better textures.
Now, as to textures. You do need to look carefully at scenery assets (and any asset really). An object with simple 'block' textures may have a great many textures which can effect performance a great deal more than an asset with one or two larger textures. There's an exception where you may want to tile the texture, but this should really be avoided unless you are working with a very large object. As always, it is up to the creator's own judgement on how they create their content, but there are ideas behind things like textures that should be looked at and then a decision made. Also keep in mind that Trainz
does support mip-mapping, and as such will reduce the size of the textures as you move away. This means that you don't
need to use objects with lower res textures further away. It will help a little with loading the asset in some cases, but if the asset can be seen up close (elsewhere in the scene/map, or even from a good screenshot vantage point), then it's not a bad thing to have a well made high res object further off, as it won't be high res when viewed from a distance.
The same applies to using object with LOD as well
Once you have one or two large texture maps on the object, you can then 'paint' the textures onto it relatively easily. At a minimum, you can paste the existing 'block' textures onto it as-is, but you can then also easily layer multiple images onto each other, creating some nice effects (even if it's just to cut 'in' a beam, or a different wood plank, or what have you). A reskinner could then easily add hand drawn shading onto the object.
The one thing that the Trainz community needs to keep in mind is that there is only so much that a game engine can achieve. The content still needs to be built to a modern spec for it to look good. True, TANE will have full world shadows, but ambient shading on objects is still essential (most game engines require this to some degree), as is a normals map, specular map, and textures that have some detail to them.
Regards