I installed Budgie flavour of Solus Linux 4.7. The apps are much snappier here than on Gnome flavour. I installed the same apps native and nix like Firefox, Opera, Vivaldi, Brave, LibreOffice, Pycharm CE, Vscode, Blender.
On Budgie: Native Firefox starts faster than nix-ed. For LibreOffice, Pycharm CE the speed is the same, there's no noticeably difference. But, native Vivaldi, Opera, Brave, Vscode, Blender starts slower than nix-ed versions. This is not a functional difference, but rather just a visual one.
Then I installed Gnome desktop on Budgie flavour Solus Linux 4.7. I wanted to see, if it's only the problem of Gnome. The results was the same, native Firefox was snappier, Libreoffice and Pycharm CE was the same, the rest of native apps was slower than nix-ed. But what I saw, all the apps starts slower on Gnome than on Budgie.
Next I installed KDE, the results was the same.
So generally speaking, it depends on the app.