many exchanges boast user stats and funding stats which don't match a corresponding increase in addresses, we can also corroborate this with the size of the exchange's known hot and cold wallets, and further corroborate this with periods of time later when many users do move funds to distinct addresses outside of exchanges, the difference with what remains on exchange we can (or have to) assume to be distinct users. finally, there have been periods of time when its not worth it to move funds off of exchange because the transaction fees would eat the small amounts that poorer/less capitalized users bought and hold.
that still leaves us with "most".
everyone knows the theoretical issues and incompleteness of this statistics collection - since there is no single public or verifiable stat to use - its pretty new to be a person that chooses assume its more likely that people are having distinct addresses on chain, than assume its more likely they're on an exchange
kind of funny how we go full circle here, but okay. hope that helps your reasoning. this article has no way of making its claims either, so there's really no point of appealing to either authority or bolster any opinion.