Yeah, I've been saying this for a few months now, thanks for going into it in such detail. Two factoids to add:
1) Seven of the eight worst teams in MLB were in the NL this year.
2) The Mets finished the season 38-22 after their deadline deals, 37-17 if you throw out their final week of coasting after they clinched. Over that period, they played all four non-Blue Jay AL East teams and lost series to TB/NYY/BOS while splitting 2 with BAL, going 4-7 overall, while they were going 33-10 against the rest of their cream-puff laden schedule. I don't think they make the playoffs as an AL team, I think they'd be in the same boat as teams like CLE and BOS, coming on strong late, but not enough to make up for the first part of the season.
Also I think it's illuminating to actually spell out the run differential by division, which makes it clear that the NL Central wasn't even the best division this year, let alone of all time:
AL East: +304
AL Central: -85
AL West: +10
NL East: -297
NL Central: +108
NL West: -40
One might argue that TOR's massive run differential skews that, which there is some truth to, but even if you subtracted their entire +221. the AL East still wouldn't be too far behind the NL Central, and if you dropped out both TOR and STL, the AL East is still way ahead (AL East: +83, NL Central: -14).