I have no sympathy for the fair-weather fan attitude.
Your personal views on what makes a good fan notwithstanding, it's a simple fact that interest drops when your team has no real hope left in the season. And even from the hardcore fan's point of view (i.e. the type of person who won't just tune out, i.e. people like you), isn't it better to have fewer lame-duck, mean-nothing games in a season? And no, jockeying for draft position does not make for interesting games.
I don't see this as particularly worse than, say, basketball, where in the Western Conference the Lakers, Mavericks and Spurs have combined for 29 of a possible 30 playoff appearances in the last decade
The difference is that basketball has twice as many playoff slots, so the Lakers dominating doesn't prevent other teams from making playoff appearances. Now, how good the Lakers have been
in the playoffs recently has arguably been bad for the game, but at least that's not a fault of the system itself.
I'm not going to let a single-season anomaly stop me from disliking the idea that a sub-.500 team can make the playoffs.
And what's wrong with that? It seems much more wrong when a team can go .600 and still not make the playoffs because 3 specific teams (two division leaders and a wildcard) happened to be better.
Regardless, in hockey/basketball, 16/30 teams make the playoffs, so you can't go much under .500 and still make them. Quibbling over the difference between 470 and 500 seems pointless.
And prior to that they averaged 65 wins a year between 1985 and 1990. You can criticize Atlanta for a lot, but they got to their power status through the draft and farming pitchers rather than just buying players.
Nowhere did I criticise Atlanta. However, because of their dominance, during those 11 years, if you played in the NL East you couldn't make the playoffs short of a one-per-league wildcard berth, which is a shit deal for those teams.