Being woefully new to LoL, I'm not sure if I'm experiencing something similar as I'm not daring to try to get into any kind of Ranked games.
But after I hit Summoner Level 30 I suddenly found myself playing in SR games with Summoner level 100+, Summoners with 100k+ Points on individual champions, games where my skill level is massively below the skill level of others and quite often it's probably better for everyone on my team if I just quit the game instead of feeding the opponents. At level 29, I was cruising along as a Miss Fortune main, getting stats like 20/10/5 on a regular basis, winning about half the games. (not ALL my games were that good, but I was normally ending with noticeably more kills than deaths)
Hit Level 30 and BAM! A good game is now something like 1/10/11, I'm spending 5 straight minutes in game standing at my turret waiting for the Minions to come to me so I can farm them because the moment I leave the safety I'm getting ganked by the Laner and the Jungler (who weren't in the lane for that 5min, but were in Mid and watching for me to leave my turret so they can come gank me), etc. Games are being won at about the same rate (slightly lower, but not massively lower), but I'm barely contributing to them. The best I can say I'm doing is that I'm annoying their Laners and Junglers by playing so passively, and I'm forcing them to farm Minions instead of ganking Champions.
Yeah, I know I'm a newbie, and not all that skilled yet - but going from Level 29 to Level 30 was like falling off a cliff. It's like Riot was saying "Okay, you've had a few months of fun playing PvP, now it's time for you to go back to playing against Bots until you git gud enuf to play against real people again."