AFK's for games

So I had a question Riot. I was just playing ranked cuz ya know, it's fun to try hard and things. We had a solid team going, 5-8 at about 25 minutes, we weren't doing too poorly. Our Sion decides to leave. Zero text saying why, no clue. He "reconnects" twice as the prompt on our screen told us, yet immediately got DC'd again for the rest of the match. It is now a 4v5. In game, your surrender tool only requires 3 votes. The game itself knows that there is someone afk. We end up losing because the enemy team finds out he's been gone for a while and decides to split push hard and take baron. Nothing we could really do. We get to the end of game lobby, Sion's name is Red indicating he left or was afk. So once again, your game knows that it was an unfair match (4v5). So I have to ask... why does this then count towards LP or series matches? If your game can already recognize that people are afk or DC'd or whatever, why is it that I am being punished for this or basically being told to "get gud" when that game had nothing to do with individual skill? When can we see a system that actually works properly in doing loss prevention for unfair games?

Sincerely,

A guy who has lost 3 series in a row due to people being AFK.