It comes down on what is important to you.

Debian is great when you're a bit more conservative and want to not change as much, and Fedora is more leading edge for new technologies. They implemented, for example, Wayland, Pipewire, and much more, as one of the first.

So, where I hope Silverblue will be a clear improvement

Don't fixate to much on SB. There's also VanillaOS out there, which is/ will be based on Debian and aims to be as user friendly as possible. Many of the pros are universal to most immutables.

• Containers for work stuff (At the moment I use whole VMs, which was one of the reasons to automate everything with Ansible)

You can already use Distrobox or Toolbx on Debian. But they don't replace VMs and are more similar to Flatpak, giving you mostly runtimes and dependencies, but the host OS is still perfectly accessible.

Fedoras polish for Gnome users

Fedora doesn't polish Gnome. They only provide vanilla desktops, KDE for example is also pretty much unchanged.

Difference is, that most other distros modify their DEs, which isn't what the creators intended.

This is why, in my personal opinion, Gnome on Ubuntu sucks for example