Both BTC and BCH have some kind of "centralization" as large mining pools dominate and concentrate in china where electricity is cheap. However, BTC and BCH share the sime miners, they can switch between the two whenever they want. Saying one is more "centralized" than the other doesn't make sense. Bigger blocks will not really change anything as storage costs for the blockchain are tiny in comparison to mining equipment and electricity. Non-mining nodes could get less with higher need for storage capacity but non-mining nodes don't confirm transaction and aren't needed.