A hard reset will only exemplify the already-existing problems in League's matchmaking.
Ranking is based solely on win or loss.
Generally, it's not the team with the best player who wins, unless they are at a massively higher skill level than their opponents. It's normally the team with the worst player(s) that loses.
We all saw this during the recent ranked mess, such as a game I saw where one team had a Diamond player but lost against a team of Gold/Silvers because s/he had a Bronze/Silver bot lane.
Already, a lot of games are one-sided stomps one way or the other because the skill levels of the various players are so disparate. Forcing a hard ranked reset will just make that even worse. It will make every team filled with 5 random players of completely different skill levels. The one that randomly has 3 Diamonds and two Golds will win against the one that randomly has one Master and four Bronzes.
Eventually, each individual player's skill will allow them to rise, given enough games, but the majority of games for a long time will be completely random and also one-sided stomps based on who was assigned to which team.
People will take forever to reach their actual skill level because ranking is based solely on win/loss, and the outcome of games will be heavily influenced by randomness.
That's not to say that this doesn't already happen at some level in most tiers of ranked, but a hard reset will just make the problem ten times worse.