How much is not withdrawing from SN similar to not withdrawing from an exchange?

Until the sats are on your node, there is an extra risk. And similarly, the same argument about the added liquidity (by keeping sats on SN) can be used by any exchange. The history shows in the end people lose if they trust and want to support a project, no matter if it is SN or an exchange.

A healthy and fair environment suitable for a Circular Economy would allow all participants to hold their sats. This will also be good for projects like SN in the end as well, simply because it will be as easy to send out (withdraw) as to send in (fund).