I disagree, see my mem and pitch number 4.
Do you observe the color of the border for every window? Do you think before running anything, where exactly you are doing that? Do you plan which qubes should have access to which websites or data? If you don’t, then it’s as simple as GNU/Linux but also as secure as GNU/Linux.
Furthermore, did you ever try to configure VPN on Qubes OS and on Linux? Are you using Bluetooth with sys-audio? If you do it the easy way, it’s again as secure as on GNU/Linux.
(Well, maybe, it’s still a bit better, if you at least use sys-usb, sys-net and sys-firewall.)
No, but you have to change how you use the OS nevertheless: you have to compartmentalize your data and apps.