But last time I tried kde/plasma, I couldn’t pull it off and went back to gnome.
KDE allows for flexibility and choice about such animations. I dislike that sort of thing and disable them all, so I don't know how well the various options work, but I do know they're there.
I don't know about transitions or anything. I don't use transitions, so ... no idea. i3 just instantly switches between monitors or workspaces etc, though maybe someone has implemented transitions like they did with gaps? Again, no idea.
[1] https://userbase.kde.org/Tutorials/Using_Other_Window_Manage...
It looks like that last session only shows up when there are multiple monitors, which is why I could not find it on my laptop.
I think it would be very rare that someone would give configurability as their reason for leaving KDE / Plasma for Gnome. If anything, people tend to complain that KDE is too configurable.