Nobody really has the time machine you’d want for a totally accurate picture of the pre-history of our system. To me the biggest single clue is the thing about the axis tilts. Van Flandern might have been right about fissioning being the general source or a general source of new planets but the thing about Earth, Mars, Saturn, and Neptune having tilts in the narrow 23 - 28 degree range does indicate a likelihood of their having been captured as a system.
The narrow range of axial tiltes for some of the planets also fits an (more than one) unstable rotation model.