You are wrong. Although centralized exchanges have many flaws, from vulnerability to hacks, inside jobs or bankruptcy, although they ask for KYC, the higher volumes and liquidity will still be there for a good number of years.
The day traders, which compose a very big chunk of the volumes, will always go mostly for off-chain trades, because there the sum of fees is smaller than the sum of tx fees for too many small trades. And for higher volumes some of the exchanges even make a discount on the fees.