It's one bad thing to sync all one's email to the their cloud. It's another bad thing to give the cloud the credentials to sync one's email directly. So in theory even if you stop using the client they can still get your email without your knowledge and explicit permission (ie you are not using the client and would reasonably expect they don't have access to new emails).
Also the cloud service now have the capability to save then retrieve the credentials in plain text making them a rich target for being compromised.
Also the cloud service now have the capability to save then retrieve the credentials in plain text making them a rich target for being compromised.