It's probably fairer this way, considering all the protection against demotions that are in place. As it stands, if people manage a lucky streak, it's quite possible for people to get promoted to a tier/division that is beyond their 'true' skill level, but be able to stave off demotion for a relatively long time even as their mmr falls to increasingly unfortunate levels.
(This is part of why some people reach gold 5 in a season, and then when next season rolls around they do fine in placements, and then get horrified as they're placed bronze. People look at their rank and feel that that's what they 'are', but far too often their mmrs [which is a truer reflection of their skill] are somewhat lower and reality bites them when placements put them closer to where they belong.)