Everything relative.
Xfce is still lightweight; the proprietary DEs take what, 2-3 Gb. < 700Mb for a fully operational DE is still light as heck.
Xfce is also noticeable snappier than both Gnome and Plasma. It responds quicker.
I don’t know Deepin’s numbers but as far as I know the heaviest DE at the moment is Cinnamon, being built on a version of Mutter that isn’t the latest. So for Mint users Xfce is definitely a more lightweight option than Cinnamon.
Also, of course, there is the truth that “Unused RAM is wasted RAM” and a very low footprint at boot looks cool on screenshots, but unless you actually have any issues what matters is how the system behaves after hours of uptime and proper usage.