This is correct and I agree.
Emails are not private by design - even if you encrypt your whole mailbox, still, 99% of users have no idea about PGP and are not wiling to setup one just to communicate with you. Not saying that many services are actually automated, for example, when you book a driving test, or receive a bill from your utility company.
So once you send an unencrypted email to anyone, or they will send you an unencrypted email, it is going to be scanned anyway on its way, no matter how secure or private your own mailbox is. Imagine getting an email from your broadband company, it clearly has your name and account number so Big Brother will know your name, that you own this email account and that you have an account with the provider in question.
Also, we have absolutely no control on other party's email account - if they use any privacy offending service, then their emails (including the ones you sent to them) are going to be scanned anyway. Or worse - if their email account will be hacked then the hacker will be able to see our email sent to them. Funny enough, not everyone is bothering or know how to secure their accounts so many accounts do get hacked from time to time,
So at this point our main advantage in using a secure email provider is that the provider itself is not going to scan our emails for profiling, marketing, etc. Everything beyond that is very hard to achieve and is most likely unrealistic unless both parties use PGP and a good, secure email provider.