I have considered the possibility (hypothesis) that the system of selecting your role might have the downside of not equally matching Elo as efficiently as it was previous seasons due to role preference and new changes, hence, deluding itself (passively) in a larger error margin across tiers.
And then, the question arises: but why do we experience this now?
Short answer: New Tiers added, less playerbase playing at the moment due to Rank instability, and Smurf accounts.
Long answer: The Elo scrambling of those who where B5, S5, G5, P5, D5 resulted in some sort of synthoms that declined in MMR 'clamps' that extend across the provisional matches and normal rank matches, including Flex matches. These clamps or 'disturbed strange LP gains' will hit you hard until you either: Reach the lowest rank for it to even itself (this is just a guess, might not work) or, Struggle your way until it's magically fixed by jumping Tiers (also a guess, might not work).
i.e. The jumping Tier 'unclamp' hypotesis: iron 1 to bronze 5, bronze 1 to Silver 5, Silver 1 to Gold 5, etc.
You can also consider that i am just a madman and that Rito has driven me into insanity. And i would perfectly agree with that 200% AD scaling mixed with True damage with a double crit chance passive efficiency