I think this is just a problem in the phrasing of the FAQ document.
The author probably means “connections for which TLS is always mandatory, such as on port 465, are safer than connections which use STARTTLS for optional TLS, such as on port 25”. An easy misinterpretation of the FAQ text is “using plaintext is preferable to using STARTTLS”. But I think the author means “requiring the use of TLS is better than optional TLS”, not “avoiding the use of TLS is better than optional TLS”!
In most e-mail software, TLS is always optional on port 25, whereas it’s always mandatory on port 465, if the software can be configured to use port 465 at all.
This doesn’t mean that STARTTLS is worse than unencrypted e-mail or that STARTTLS shouldn’t be used when the server advertises it.
EFF is working on an experimental approach to improve the security of STARTTLS and make it more similar to TLS-required methods of transferring e-mail.
A related technology is MTA-STS
https://tools.ietf.org/html/rfc8461
These help to make STARTTLS work more like what I think the FAQ author would like to see. 