Experience is not a great way to judge accounts exactly. All it does is track games after it got introduced. Mastery scores are also janky, because mastery predated the EXP/BE system there's folks with a pretty low EXP level yet insane amounts of Mastered champions compared to others at their Experience.
Each Que has its own MMR. So if some folks grinded their skill and EXP in a different que then moved to normal, they will pub stomp. Vice versa some one who got really, really, really good at the game by mastering mechanics and champions in norms should be able to take it to ranked and be above their starting MMR.
Remember that every time there is a soft reset it rolls back players, so the gains of pubstomping 10-15 games might not be enough to move that player out of a low MMR range.
Its been suggested that Riot adds a soft cap for normal. To reduce super high elo folks getting into games vs people who will suffer for the mismatch, and to remove super low elo folks from losing teammates games.
Ultimately because of Kfactor MMR systems do account for skill mismatches, but they never quite remove them. Your system should to look at how many games are played in the que and MMR does this by filtering out the players who consistently stomp at their level or Throw matches constantly.
I made a giant post on MMR and Elo systems yesterday. Check it out if your curious about them. (shameless plug, but I made it to actually help folks)
You don't need to read it unless you want, its a lot of text. I am happy to explain stuff to the best of my ability and reply directly to your questions in this thread if that's your preference. Just might take me a while.
