Link to Riot officially stating that the ammount of Rewards stays approx. the same:
I believe them.
Im already used to only getting "real" rewards from leveling up thanks to Overwatch and CS: GO where the system is quite similar.
Further i do see the XP Gains in the new Level System as some kind of IP Gain substitute. Its a progress on the long way to gain sth new and shiny
(e.g. new champions) so i dont have the bad feeling of gaining nothing from finishing a game.
The gain in the old system towards a 6300 champion were slow and so are the ones in the new system.
Like, i got compensation BE at the start and bought 5 champions that i always wanted. Im playing 2 games a day (mostly ARAM),
i dont always get First Win of the Day Mission/Reward and i already own most of the champions i like. (Playing since season 5 i believe)
And im fine even if Riot would really try to make more money from Champion buys due to the removal of Runes and introduction of Hextech Crafting.
Im not playing this game to get every skin and every champion. Im playing it for fun, casually and dont need instant-rewards to keep on playing.
I like the Lore, the Design, the Championships, the Reveals. I dont need everything at once or as fast as possible.
So yeah just my view on the changes.
(Feel free to downvote the honest opinion of a simple player. This is my personal truth and while you may not agree with everything, not an inch of it is a blatant lie or a wrong fact. Its just an opinion))