First off, I fully agree that the rewards that are given out are too high and need to be cut back somehow in order to make things more sustainable. In that regard, I don't mind getting fewer rewards from my Level 5 accounts which now reaches Champions 1 & my level 3 account that reaches Champion 2. I do want to be able to get matched with players who have higher level cards though as outplaying those is one of the biggest joys of the game.
My main fear with these changes is that the new player experience will be absolutely horrible. So they will spend 10$ on the summoner's spellbook and be totally stuck in Bronze 3 without any sense of progression unless they start spending more?
The way I look at it, 95%+ of players (including myself) are completely potato when it comes down to the willingness for any mental effort and the main reason they start playing the game initially is for the rewards. Right now, at least there is a sense of progression when starting to play as rewards increase a bit when reaching a higher level. These changes would completely kill this dopamine mechanic.
Wouldn't it be better to just lower the rewards at low ranks and introduce the collection power requirement further up in the rankings? Maybe introduce some one-time rewards to unlock for new players that get the summoner's spellbook to get them going. Play a certain number of matches unlocks rewards, play (future) tutorial unlocks reward, Buy card on the market unlocks reward, ...
With the current suggested model, I really feel the onboarding of new players getting sold and hooked on the game will be non-existing anymore.