By restating your question I would reply by asking, "How tough will it be
for ND to finish the regular season undefeated or with only one early-season
loss?" I believe that is the heart of the matter. I don't believe it is
highly likely at all that ND will accomplish that great feat with Brian
Kelly still as head coach, with a defense that must be reconstituted,
with no special teams effort at all, and with unclear choices about how to
run the offense with undecided quarterbacks.
Simplifying all your excellent, detailed analysis, it is apparent that no
team is likely to reach the top-six ranking with two or more losses in any
season, especially for ND in order to overcome the bowl bias that we face
for the prior twenty years of bowl results.