Mexican Soccer Premier League's Relegation System Questionable

In professional league soccer, during the regular season, standings are determined by the point system.  If your team wins a game, they get 3 points, lose and they get 0 points.  If a draw occurs, then each team gets 1 point added to their total.  In most leagues around the world, if there are one or more lower-level leagues around in a country, they have a process called "promotion and relegation" that rewards the lower league champions and punishes poor performance in the upper league.  In it, the worst-performing team(s) from the higher league in a particular season is/are demoted (or regulated), while an equal number of outstanding teams from the lower league get promoted. So in English soccer, we have three teams, Burnley, Queens Park Rangers, and Leicester City, who are at the bottom of their 20-team Premier League standings as the current 2014-15 season is winding down.  If nothing changes in the standings, they will be relegated for next year to the second-tier Championship League, while the top three teams in that league will get a shot at the Premier League.  I like the relegation system as it makes the late-season games more meaningful and that teams which aren't doing well can't just write off the season and expect to be rewarded with high draft picks, as is the case in many American professional sports leagues.  Unfortunately, in America, there is no relegation system as of yet in professional soccer, although there are three tiers of leagues here.  In Mexico, there is relegation, but the system seems confusing and unfair to me...

The top-tier Mexico pro soccer league is called Liga MX, with 18 teams in it.  They annually promote into it the winner of the second-tier league Ascenso's championship from the previous year and send back, through relegation, their own most poorly-performing team.  But in the Liga MX, relegation is determined by going back from three entire years of a team's performance and calculating the average points per game it has.  If a team has been in the league less than that time, like the newly promoted Universidad de Guadalajara Leones Negros, only the time they've been in the Liga MX is counted.  So a team like Morelia, which did well three years ago and tabulated a lot of points back then, but is by far the worst team in the league this year, hopelessly rock-bottom in the standings, is safe from relegation because its three-year average is higher than others.  Puebla and the Leones Negros, on the other hand, are doing reasonably well this year, far from the worst in the league...yet it is they who are battling each other to avoid demotion.  Puebla is actually the last in the relegation table right now, meaning that were the season to end today, they would be relegated down to Ascenso.  But at the same time, they are also in position to qualify for the league championship playoffs for the winter/spring Clausura season...and could conceivably win the Liga MX championship for the 2014-15 season while at the same time be demoted to the next lower league!  Now there is something  awfully, awfully wrong with such a system...