Yes — these results are consistent with an internal alignment problem, most likely a lens element that is de-centered and/or out of proper spacing.

The pattern fits common aberration behavior:

• Softness increasing rapidly at wider apertures points to spherical aberration becoming more visible.
• Different rendering toward the edges, including doubled detail, suggests off-axis aberrations such as astigmatism.

Together, that strongly suggests something in the optical group is not sitting where it should be, rather than the lens simply being an old or inherently soft design. The slight rattle could support the idea of a loose internal part, but the test images are more meaningful evidence than the rattle alone.

Because another copy of the same lens performs properly, this copy is almost certainly defective rather than just characterful. Repair may require optical realignment, which is often fiddly and not always economical. If it has little resale value as a normal lens, it makes sense either to sell it honestly as defective/soft-focus-character, keep it for creative use, or experiment with disassembly if you're comfortable risking it.