If the sender is using GMail, then using your own mail server is less secure than using GMail as the receiver.

Sure even though, as most others, my server supports TLS, having your email not leave gmail at all may be slightly more secure. Part of the point however was that when either server or receiver is using Gmail, your possibly confidential email content is still in Google’s hands. Using a personal server reduces that part of the attack surface. Still this does not mean I vacate my overall point that email in general is suboptimal from a secop standpoint.