Haven’t had a samsung phone since the note 3, but I remember having issues with unlocking the bootloader, I think you had to use some 3rd party tool because samsung provided no guide in their manual. With nexus and pixel phones it’s really easy so them I can definately recommend.

According to wireguard itself the kernel-module based backend is more efficient/faster than the userspace implementation, and to use that it still requires root.

Adaway of course, and wireguard via the proper kernel module.

Mine has always been super snappy, so something’s definately off I’d say.