I'll agree as far as matchmaking is concerned. There's no reason why someone doing placements should be in the same queue as someone doing promos. That has the potential to put you at a disadvantage. But I also don't think this is a particularly egregious degree of int. I'm not saying that the Sion didn't troll, but I also don't think he was** the **reason why you lost (purely from looking at the post game stats). For example...
-your midlaner only had 3.9 cs/min as Ahri, which is pretty awful considering that I play midlaners with less waveclear and farm better in similar elo
-your adc didn't farm either
-support Morgana died 10 times (also built Righteous Glory instead of Zhonyas which is truly beyond me)
-you only built 1 MR item against a super fed Veigar (I understand why you'd stack a lot of armor against their team though - I presume Veigar got fed later on)
my point is there's a lot of reasons why you lost that game aside from Sion. By your ADC and midlaner literally not farming they're losing a lot of gold and making the game harder for you to win. Also Morgana's build being completely horrible etc. etc. I've had my share of games w/inters, griefers, trolls etc. but this is far from the most egregious example (imo)