From the looks of it, you are playing in a group that is like high silver/gold elo, and its putting you against other groups. The Jarven in your zed game was like in a group of 3. The D5 jax in your lee game was with ashe.
From looking at OP.GG in my matches, the making tries to balance out the overall MMR of both teams. For an example, I was in a 5 man with my friends who are all silver 1 or gold 5. I'm diamond 5. The enemy team was 1 plat, 2 high gold, 2 bronze, and over all, the MMR average was pretty even. We lost that match though rip
It really just seems like when you're in a group, you might run into that other group whos platinum along with their bronze friend. Then all hell breaks loose in the matchmaking. Thats looks like what happened to you lmao!
http://imgur.com/a/WkDnJ
It makes sense on paper, but in reality it can become a coin flip from snowballing
Running into two diamonds though, that's just bad luck. They must have had lower normals MMR for whatever reason.