But what if KC played the Rams, Chicago, and Atlanta this year in the NFC, and Buffalo got Philly, Dallas, and SF? Three easy wins vs. three difficult games, which could affect the first tie breaker: overall record. At least when a team plays one non-conference division in the entirety, there is a better chance they will be facing a good team, as each division has one (well, except this year with the NFC South, lol).
Also, under your proposal, we should just eliminate the divisions then.