he issue lies in the abuse of the system
if you are given loss prevention or lose less LP whatever the case is then people will abuse it.
someone does badly and feeds, well this player ( kindly agrees , LMAO flamed into is more likely) will afk/dc and then the team instead of losing and losing lp they get a lost prevention
the way it is now it effects everyone the same, every one deals with the player afk/dc and loses the LP so if every one deals with it, its fair overall.
yes someone can in theory have this happen more then another random person but its a safe estimate that this only comes up in 8-10% of games. so over 100 games if this happen 8 times and you still win 52 games you have a positive win rate and you climb.
your climb/rank isnt going to be that dramatically effected by 8% of games over the course of a season . it wont make the difference from being silver ( or lower) to diamond.
either you can climb or you cant.
there is a reason why the same people end up diamond + every season. they are better. regardless of meta, strategy, afk/trolls/ inters