I guess you can think of it that way, but it probably depends on the technology used by the printer at that point. My thought was that for the 3d printer, at least it's one consistent piece with no seams or edges that are later welded together. The welds can have imperfections/weaknesses and need to be inspected. Materials can also have weaknesses and imperfections, either on a batch level or individual area level, and need to be tested/inspected. For a printed piece, I would expect the strength to be generally consistent throughout the piece (of course still might be weaknesses based on design shape, thickness), but of course, you'd still want to inspect it.
PS - totally not an expert on 3d printers or materials or welding
I am not an expert on either, but in general 3D printers lay out the material in thin layers (with each layer laid out line by line). Thus you have lots of potential seams everywhere two points laid at different times touch.
I think modern technologies prevent seams forming at most of those points, but the potential (impurities, dirt, etc.) still remains so must be tested.
I could imagine some technology that takes advantage of future layers not being there yet to validate the most recent layer on the same pass, and the one that the current layer will be built upon (as that might have suffered in the time since it has been laid) in a way that is exclusive to this manufacturing method. But as you move to bigger and bigger one-piece parts, you would probably also want your process to support undoing a few layers on failure detection to forego scrapping the whole part.
PS - totally not an expert on 3d printers or materials or welding