Earlier quoted context omitted.
To be honest I haven't owned a dGPU in almost 20 years, but I've been lead to understand that most users with them use them all the time and ignore their iGPU, unless they're laptop users, in which case they might have to use Nvidia's proprietary drivers from what I understand; the installation of which is something Mint makes straight forward for novices, or so I've been lead to understand. Maybe I'm wrong about som…
So Debian is a no because it ships with KDE? Imo Ubuntu deserved to lose its users when they switched to Unity, not because Unity sucks (it does) but because it's unacceptable for a newbie-focused OS to rug-pull its entire GUI like that for any reason. But it's still #1, so realistically the leader is going be either Ubuntu or something corp-supported like SteamOS.
I don't think this is a problem at all. I tend to install Debian from the command line (Arch-style), but from what I remember GNOME is the default DE. DEs are largely a matter of opinion, but I find GNOME to be more polished overall. I do use a few extensions however to recreate a desktop-centric UX (Dock, boot to desktop and a few other tweaks).