I will admit to not being a lens designer myself, so what was said about optical node location can well be true...consider that in SLRs the various brands had different distances between lens mount and film plane...FD lenses from Canon have more distance than newer EF lenses. In the case of digital sensors, there is already a 'handicap' true of digital, that the angle of light rays can not be as great as for film, so designers have to try to get light rays to strike at less of an angle, yet the shallower distance of the thinner mirrorless body goes in the wrong direction relative to that goal of lessening the angle of the light rays. Hasselblad, for example, took advantage of film tolerance of greater ray angle and shorter node-to-fim-plane distance in producing the Hassy SWC with 38mm lens, which has higher perfomance optically than the Hassy 40mm lens which has a retrofocus design.
In the case of longer FL, the comparisons published on web sites by folks does seem to point to the 'thinner body, longer lens barrel' truism, nevertheless.